ChatGPT answers, unedited

If your core requirement is “a user does X on my website → automatically send a personalized email/SMS → branch based on what they do next,” I’d shortlist these:

My practical recommendation

Customer.io is probably the first one I'd evaluate for a custom website or SaaS product. Its Journeys can trigger from arbitrary customer events, segment membership, forms, dates, webhooks, etc., and branch based on subsequent behavior. It supports email, SMS, push, in-app, WhatsApp and webhooks in the same journey. Customer.io Customer.io Customer.io

For example:

User views pricing page → wait 30 minutes → email personalized to the plan they viewed → if they start checkout, stop → if they don't, SMS reminder 24 hours later → if they purchase, enter onboarding journey.

Klaviyo is particularly compelling if you're ecommerce-focused. Its flows can be triggered by events such as product views, checkout, purchases, and other tracked behavior, and event properties can be inserted directly into email/SMS personalization. Klaviyo Help Center Klaviyo Help Center Klaviyo Help Center

Braze is worth considering when you're building a sophisticated, high-volume customer-engagement system. It supports real-time behavioral triggers across email and SMS, plus web, in-app, push and other channels, with extensive segmentation and experimentation. Braze Braze Braze

The key distinction

I'd choose based on what your site actually is:

• SaaS / web app: Customer.io
• Ecommerce / Shopify: Klaviyo
• Large consumer product with complex omnichannel engagement: Braze
• Highly technical team wanting maximum control over event-driven messaging: Customer.io or Braze

One important consideration is your event pipeline. The software needs to receive clean events such as signup, pricing_page_viewed, trial_started, feature_used, checkout_started, and purchase_completed. Customer.io explicitly supports event-triggered automations and event-property conditions, while Klaviyo uses event/metric-triggered flows. Customer.io Klaviyo Help Center

If you tell me (1) SaaS vs ecommerce, (2) approximate monthly active users, and (3) whether you need transactional as well as marketing messages, I can narrow this to the most appropriate 2–3 options and compare pricing/integration architecture.

User views pricing page → wait 30 minutes → email personalized to the plan they viewed → if they start checkout, stop → if they don't, SMS reminder 24 hours later → if they purchase, enter onboarding journey.

Klaviyo is particularly compelling if you're ecommerce-focused. Its flows can be triggered by events such as product views, checkout, purchases, and other tracked behavior, and event properties can be inserted directly into email/SMS personalization.

For your use case—“when a user does X on my site, send a personalized email/SMS”—I’d look at customer-engagement platforms rather than generic email providers.

The main options

My practical recommendation

If you're a SaaS/web app: I'd start with Customer.io. It is explicitly designed around profile + event data, so you can do things like:

user_signed_up → wait 1 day → hasn't_completed_setup → email

or:

viewed_pricing → wait 2 hours → no_purchase → SMS

Customer.io supports email, SMS, push, in-app/web messaging and webhooks, with automations driven by the behavioral events you send it. Customer.io

customer.io

If you're e-commerce: I'd lean toward Klaviyo. Its flows are particularly well suited to events such as product views, checkout starts, purchases and inactivity, and it can combine email and SMS within the same behavioral flows. Klaviyo Klaviyo Help Center

klaviyo.com

If you're a larger company with sophisticated cross-channel journeys: Braze is worth evaluating. It supports real-time behavioral triggers, personalized email/SMS, segmentation and journey orchestration across additional channels such as push and in-app messaging. Braze Braze

braze.com

One important distinction

If what you really want is something like:

“Give me an API/SDK where I send user events, and marketers can build arbitrary journeys from those events.”

then Customer.io / Braze are particularly aligned with that architecture.

If instead it's:

“I run an online store and want abandoned cart, browse abandonment, welcome, post-purchase, winback, etc.”

then Klaviyo is a very natural fit. Klaviyo specifically supports metric-triggered flows using behavioral event data and dynamic event variables. Klaviyo Help Center Klaviyo Help Center

If you tell me (1) SaaS vs e-commerce, (2) roughly how many users/messages per month, and (3) whether you need the developer to define events or marketers to build journeys, I can narrow this to 2–3 options and compare pricing, implementation effort, APIs, event tracking, and deliverability.

If your core requirement is “user does X on my site → send a personalized email/SMS → branch based on what they do next,” I’d shortlist these:

1. customer.io — best overall

• Built specifically around behavioral/event-driven messaging.
• Supports email + SMS + push + in-app in the same workflow.
• You can trigger journeys from events such as page views, cart abandonment, purchases, form submissions, etc., and branch based on subsequent behavior. Customer.io Customer.io
• Particularly good if you have a SaaS/product-led website and developers can send events into the platform.
• My pick for most teams building this from scratch.
• klaviyo.com — best for ecommerce

• Excellent for product/catalog data, abandoned carts, browse abandonment, purchase follow-ups, segmentation, and promotional messaging.
• I'd favor it over Customer.io if your business is primarily Shopify/ecommerce/DTC.
• braze.com — best for large-scale consumer apps

• Extremely powerful cross-channel orchestration and personalization.
• Strong choice when you have substantial behavioral data, mobile apps, sophisticated lifecycle marketing, and a larger marketing/engineering team.
• Usually more platform than a small or early-stage company needs.
• iterable.com — strong enterprise alternative

• Good omnichannel journey orchestration and segmentation.
• Worth evaluating alongside Braze for a larger marketing organization.

What I'd choose

Customer.io is especially well matched to the exact use case you described. Its workflows can react to website/app events and combine email and SMS in the same journey, with conditional branches, delays, personalization, and conversion tracking. Customer.io Customer.io

For example:

User signs up → wait 10 minutes → email personalized onboarding → if they haven't completed setup after 24h → SMS → if they visit pricing → send a different email → if they purchase → exit the campaign.

Customer.io supports event-triggered automations specifically for behaviors such as abandoning a cart, viewing a page, or completing an order. Customer.io

If you tell me what your site does, approximate monthly active users, and whether it's ecommerce or SaaS, I can narrow this to the best 2–3 options and compare pricing, implementation effort, event tracking, email/SMS costs, and APIs.

If your core requirement is “a user does X on my site → send a personalized email/SMS → branch based on what they do next,” I’d shortlist these:

1. Customer.io — my default recommendation

Customer.io is particularly well suited to event-driven product messaging. You send it events such as:

• signed_up
• viewed_pricing
• started_checkout
• invited_teammate
• created_project
• subscription_expiring

Then you can build journeys that react to those events and branch based on subsequent behavior. It supports email, SMS, push, in-app, webhooks, and more. Customer.io Customer.io

For example:

User views pricing → wait 2 hours → email personalized to the plan viewed → if they return to pricing, send SMS → if they subscribe, exit the journey.

That's exactly the kind of workflow Customer.io is designed around.

2. Klaviyo — if you're selling products

Klaviyo is excellent if your site is an e-commerce business. Its flows can use events such as Viewed Product, Started Checkout, and Placed Order, and those events can populate personalized content in messages. Klaviyo Help Center

It supports automated email + SMS + push flows triggered by customer actions. Klaviyo Klaviyo Help Center

I'd pick it over Customer.io for something like:

Viewed $200 shoes → abandoned cart → SMS reminder → email with the exact product → purchased → post-purchase sequence.

3. Braze — if you're operating at serious scale

Braze is the heavyweight option. It supports real-time behavioral triggers across email, SMS, push, in-app, web, WhatsApp, and other channels, with sophisticated journey orchestration and experimentation. Braze Braze

Its email and SMS products explicitly support real-time behavioral triggers and dynamic personalization. Braze Braze

I'd consider Braze when you have a substantial user base, complex lifecycle programs, and a team dedicated to growth/CRM.

What I'd choose

SaaS / web app: → Customer.io

E-commerce: → Klaviyo

Large consumer app / enterprise: → Braze

CRM + sales + marketing in one system: → HubSpot

One important distinction: I'd favor Customer.io/Braze over a traditional email marketing platform if your definition of “personalized” means arbitrary events from your application, rather than just things like purchases and abandoned carts.

If you tell me what your site does, roughly how many users you have, and whether you're B2B SaaS/e-commerce/B2C, I can narrow this down to the best 2–3 and compare pricing, implementation effort, APIs, event tracking, SMS costs, and personalization capabilities.

If your core requirement is “a user does X on my website → automatically send a personalized email or SMS”, I’d shortlist these:

*SMS availability and capabilities depend on configuration/region.

🥇 My default recommendation: Customer.io

Customer.io is probably the closest match to what you're describing.

You can send events such as:

user_signed_up
pricing_page_viewed
trial_started
feature_used
checkout_started
subscription_cancelled

and build logic like:

User starts trial → wait 2 days → if they haven't used Feature X → send personalized email → wait 1 day → send SMS → stop when they complete Feature X.

It supports email, SMS, push and in-app messaging, with workflows driven by real-time behavioral data. Customer.io Twilio

customer.io

🛒 If this is ecommerce: Klaviyo

Klaviyo would be my first choice if you're selling products.

It's particularly strong for:

• Product/browse abandonment
• Cart abandonment
• Post-purchase sequences
• Replenishment
• Win-back
• Personalized product recommendations
• Email + SMS coordination

Its ecommerce integrations make this substantially easier than building your own event infrastructure. Klaviyo UK Customer.io

klaviyo.com

🏢 If you're big: Braze

Braze is the option I'd look at when you're operating at substantial scale and want sophisticated orchestration across email, SMS, push and in-app messaging. It is powerful, but substantially more complex and expensive than Customer.io. Twilio Vero

braze.com

My ranking for your use case

1. Customer.io — best balance of behavioral triggers, personalization, email + SMS, and flexibility.
2. Klaviyo — #1 if you're ecommerce.
3. Braze — #1 if you're a large consumer/app business.
4. Iterable — excellent for sophisticated omnichannel marketing teams.
5. HubSpot — best if you also want CRM/sales automation.
6. Brevo — best when keeping costs down is important.

The key distinction is where the behavioral data comes from. Customer.io/Braze/Iterable are particularly good when your own application generates events such as completed_onboarding, viewed_report, or invited_teammate; Klaviyo is exceptionally good when those events are commerce events. Sequenzy

If you tell me what your site does, roughly how many users you have, and whether it's SaaS/ecommerce/lead-gen, I can narrow this down to the best 2–3 options and compare pricing + implementation effort.

and build logic like:

User starts trial → wait 2 days → if they haven't used Feature X → send personalized email → wait 1 day → send SMS → stop when they complete Feature X.

It supports email, SMS, push and in-app messaging, with workflows driven by real-time behavioral data.

If your core requirement is “when a user does X on my website, send them a personalized email/SMS”, I’d shortlist these:

My recommendation

For most companies, I'd start with Klaviyo or Customer.io.

Choose Klaviyo if you're selling products/services and want a relatively turnkey system. Its flows can trigger from behaviors such as product views, checkout starts, purchases, form submissions, and inactivity, and it supports email + SMS in the same automation framework. Klaviyo Klaviyo Help Center

Choose Customer.io if your website is more like a SaaS/product application and your events look like:

• signed_up
• created_project
• invited_teammate
• used_feature_X
• visited_pricing
• started_trial
• trial_expiring
• subscription_cancelled

That's the use case where I'd lean toward an event-centric customer engagement platform rather than a traditional email marketing tool.

Choose Braze if you're expecting millions of users, sophisticated real-time journeys, and lots of channels. Braze supports real-time behavioral triggers across email, SMS, push, in-app, WhatsApp, etc., with sophisticated segmentation and experimentation. Braze Braze

A typical setup

Your site/app sends events:

User visits pricing page
        ↓
pricing_page_viewed
        ↓
Customer.io / Klaviyo
        ↓
Wait 2 hours
        ↓
Did user start trial?
   ↙          ↘
 YES           NO
  ↓             ↓
do nothing     Email
                ↓
             Wait 1 day
                ↓
             SMS

You can also personalize the actual message using the event data—for example, Klaviyo can use event metadata to populate the specific product someone viewed or abandoned. Klaviyo Help Center

One important distinction: if this is a SaaS website, I'd probably pick Customer.io; if it's ecommerce, I'd probably pick Klaviyo; if it's enterprise/high-volume consumer, I'd pick Braze.

If you tell me what your site does, roughly how many users you have, and what behaviors you want to trigger on, I can narrow it down to the best 1–2 options and compare pricing, APIs/event tracking, SMS, segmentation, and ease of implementation.

If your core requirement is “a user does X on my site → send a personalized email/SMS based on that behavior”, I’d shortlist these:

Customer.io, Braze, and Iterable are particularly strong when you want arbitrary product events to drive sophisticated journeys rather than just traditional marketing automation. Vero Sequenzy

My recommendation: Customer.io

For a typical SaaS/web product, I'd start with customer.io.

For example, you can instrument events like:

signed_up
completed_onboarding
viewed_pricing
created_project
invited_teammate
started_trial
used_feature_X
subscription_expiring

Then build logic such as:

User signs up → wait 1 day → if they haven't created a project → personalized email → if they still haven't acted → SMS → stop the journey when they create one.

The important distinction is that Customer.io is designed around your application's behavioral event stream, so you're not forced into an ecommerce-centric data model. Hesper

When I'd choose something else

• Shopify/ecommerce: choose klaviyo.com. Its ecommerce data model and prebuilt behavioral flows are hard to beat. ClickPost
• Millions of users / sophisticated consumer app: choose braze.com. It's built for real-time, cross-channel orchestration at enterprise scale. Vero
• Large company with complex marketing journeys: consider iterable.com. It has strong email/SMS/push/in-app orchestration. Vero
• You want CRM + marketing automation together: hubspot.com is more compelling.
• You want relatively inexpensive automation plus CRM: activecampaign.com is worth considering.

If you tell me what you're building (SaaS, marketplace, ecommerce, consumer app, etc.), roughly how many users you have, and whether SMS is transactional or marketing, I can narrow this to the best 2–3 and compare pricing/implementation. trypropel.ai

My recommendation: Customer.io

For a typical SaaS/web product, I'd start with customer.io.

For example, you can instrument events like:

signed_up
completed_onboarding
viewed_pricing
created_project
invited_teammate
started_trial
used_feature_X
subscription_expiring

Then build logic such as:

User signs up → wait 1 day → if they haven't created a project → personalized email → if they still haven't acted → SMS → stop the journey when they create one.

The important distinction is that Customer.io is designed around your application's behavioral event stream, so you're not forced into an ecommerce-centric data model. hesper.io

When I'd choose something else

If your core requirement is “user does X on my website → send a personalized email/SMS → branch based on what they do next,” I’d shortlist these:

1. klaviyo.com — best if you're selling products

Klaviyo's Flows can trigger from events such as product views, checkout, purchases, forms, price changes, and inactivity, then branch based on customer attributes and behavior. Email, SMS, and push can be combined in the same flow. Klaviyo Klaviyo Help Center

It's particularly good if you want flows like:

Viewed product → wait 2 hours → email → didn't purchase → SMS → purchased → stop → bought product → cross-sell

It also supports inserting event-specific data into messages, such as the exact product someone viewed or abandoned. Klaviyo Help Center Klaviyo Help Center

I'd choose this if: you're e-commerce, marketplace, subscription commerce, or otherwise customer/transaction oriented.

2. customer.io — best for SaaS/product behavior

This is the one I'd investigate first if your website is a SaaS/product rather than an online store.

It's designed around behavioral events and lifecycle journeys, so you can model things like:

• Signed up
• Completed onboarding step 2
• Invited a teammate
• Used feature X
• Didn't use feature Y
• Hit usage threshold
• Started checkout
• Became inactive

Then use those events to personalize multi-step email/SMS journeys.

I'd choose this if: your own application generates lots of custom behavioral events and you want marketing automation tightly connected to your product.

3. braze.com — best at serious scale

Braze is extremely strong for real-time behavioral orchestration. It supports real-time triggers based on customer behavior and cross-channel journeys, with sophisticated personalization and experimentation. Its SMS product also supports behavioral triggers and dynamic personalization. Braze Braze

I'd choose this if: you're a larger company with a substantial customer base, multiple channels, sophisticated data infrastructure, and a team dedicated to lifecycle/CRM.

4. iterable.com — strong enterprise alternative

Iterable's Journeys can react to website/app actions, user-property changes, and custom events, with email and SMS among its supported channels. Iterable Support Iterable Support

Its journey system is particularly good for coordinating complex cross-channel lifecycle programs. Iterable

My recommendation

If you tell me what your site does, I'd narrow this down pretty aggressively.

As a starting point:

• E-commerce → Klaviyo
• SaaS / web app → Customer.io
• Large consumer app → Braze
• Large enterprise CRM/lifecycle team → Iterable

The important distinction is that you don't merely want an email marketing tool. You want a behavioral customer-engagement platform with an event pipeline.

For example, you should be able to send something like:

user.viewed_pricing → user.started_trial → user.invited_teammate → user.did_not_activate → SMS/email

rather than just:

user joined mailing list → email 1 → email 2 → email 3

If you tell me (1) what your website does, (2) roughly how many users you have, and (3) whether SMS is essential, I can give you a specific winner + expected pricing tier + implementation architecture.

My recommendation

If you tell me what your site does, I'd narrow this down pretty aggressively.

As a starting point:

If your core requirement is “when a user does X on my website, automatically send a personalized email or SMS”, I’d shortlist these:

Recent 2026 comparisons consistently put Customer.io, Braze, and Iterable toward the top for event-driven lifecycle messaging, while Klaviyo is particularly strong for ecommerce. Vero G2 Learn Hub Taqtics

My recommendation: Customer.io

For example, you could define events like:

Signed Up
    ↓
Viewed Pricing
    ↓
Started Checkout
    ↓
Did Not Purchase

Then create a journey:

User views pricing
       ↓
Wait 30 minutes
       ↓
Send personalized email
       ↓
Wait 24 hours
       ↓
If still hasn't purchased
       ↓
Send SMS
       ↓
If purchased → stop journey

The important distinction is that Customer.io is built around product/user events, rather than just contact lists. That makes it particularly well suited to SaaS and websites where the important signals are things like signup, viewed_product, completed_step, abandoned_checkout, subscription_started, etc. G2 Learn Hub Automation Atlas

When I'd pick something else

• Shopify/ecommerce → Klaviyo. Its ecommerce data model and revenue attribution are major advantages. Propel
• 1M+ users / sophisticated consumer app → Braze. Fantastic event-driven orchestration, but you're moving into enterprise territory. G2 Learn Hub Braze
• Large marketing team → Iterable. Particularly good when marketers—not engineers—need to build complex cross-channel journeys. Vero
• You want CRM + marketing automation together → HubSpot.
• Small team and simpler automation → ActiveCampaign.

If you tell me what your site does (SaaS, ecommerce, marketplace, lead-gen, etc.), roughly how many users you have, and whether you already use Segment/PostHog/HubSpot/etc., I can narrow this to the best 2–3 and compare pricing + implementation.

My recommendation: Customer.io

For example, you could define events like:

Signed Up
    ↓
Viewed Pricing
    ↓
Started Checkout
    ↓
Did Not Purchase

Then create a journey:

User views pricing
       ↓
Wait 30 minutes
       ↓
Send personalized email
       ↓
Wait 24 hours
       ↓
If still hasn't purchased
       ↓
Send SMS
       ↓
If purchased → stop journey

The important distinction is that Customer.io is built around product/user events, rather than just contact lists. That makes it particularly well suited to SaaS and websites where the important signals are things like signup, viewed_product, completed_step, abandoned_checkout, subscription_started, etc.

When I'd pick something else

If your core requirement is “someone does X on my website → automatically send them a personalized email/SMS”, I’d shortlist these:

My recommendation

Pick Klaviyo if you're selling products/services directly to consumers. Its flows can trigger from events such as product views, checkout, purchases, form submissions, and custom events, then branch based on customer attributes and behavior. It supports email and SMS within the same flow. Klaviyo Help Center Klaviyo UK

For example:

User visits pricing page → waits 30 min → if they haven't signed up → personalized email → if they clicked but didn't convert → SMS → if they convert → exit campaign.

It can also insert event-specific data into messages, so the message can reference the particular product/action that triggered it. Klaviyo Help Center Klaviyo Help Center

Pick Customer.io instead if this is a SaaS/web app. It's particularly well suited to sending messages from the event data your application generates—email, SMS, push, in-app/web messages, etc. Customer.io

Pick Braze if you're building at significant scale and need sophisticated cross-channel orchestration, experimentation, and real-time behavioral targeting. It supports real-time triggers for email and SMS as well as other channels. Braze Braze

If I were choosing

• Shopify/e-commerce: Klaviyo
• SaaS/web app: Customer.io
• Mobile app + very large user base: Braze
• Enterprise marketing organization: Braze or Iterable
• Small team wanting the easiest setup: Klaviyo

If you tell me what kind of site you have (SaaS, e-commerce, marketplace, etc.) and roughly how many users/month, I can narrow this down to the best 2–3 and compare pricing, event tracking, SMS costs, integrations, and implementation effort.

Pick Klaviyo if you're selling products/services directly to consumers. Its flows can trigger from events such as product views, checkout, purchases, form submissions, and custom events, then branch based on customer attributes and behavior. It supports email and SMS within the same flow. Klaviyo Help Center Klaviyo UK

For example:

User visits pricing page → waits 30 min → if they haven't signed up → personalized email → if they clicked but didn't convert → SMS → if they convert → exit campaign.

It can also insert event-specific data into messages, so the message can reference the particular product/action that triggered it. Klaviyo Help Center Klaviyo Help Center

Pick Customer.io instead if this is a SaaS/web app. It's particularly well suited to sending messages from the event data your application generates—email, SMS, push, in-app/web messages, etc.

Pick Braze if you're building at significant scale and need sophisticated cross-channel orchestration, experimentation, and real-time behavioral targeting. It supports real-time triggers for email and SMS as well as other channels.

If I were choosing

If your core requirement is “user does X on my site → send a personalized email/SMS based on that behavior”, I’d shortlist these:

1. Customer.io — my default recommendation

customer.io

I'd start here if you're a SaaS or web product.

You can build journeys around events such as:

• User signs up
• User visits a particular page
• User starts but doesn't complete an action
• User reaches a usage threshold
• User hasn't logged in for 7 days
• User becomes a high-value customer
• User performs event A but not event B

Then branch the journey based on attributes/events and send personalized email, SMS, push, and other messages.

The big advantage is that Customer.io is designed around event data + lifecycle automation, rather than being primarily an email newsletter tool.

2. Braze — best if you're scaling

braze.com

Braze is considerably more powerful for sophisticated customer journeys. It supports real-time behavioral triggers, personalized email and SMS, cross-channel orchestration, experimentation, and predictive/AI functionality. Braze Braze Braze

I'd choose it if you expect things like:

Website event → determine customer segment → wait 2 hours → email → if unopened, SMS → if clicked but didn't purchase, change offer → personalize based on previous behavior → optimize channel/time automatically.

It's excellent, but generally more platform than a small team needs.

3. Klaviyo — best for ecommerce

klaviyo.com

If you're selling physical products, I'd seriously consider Klaviyo before Customer.io.

Its flows can trigger from things like product views, checkout, orders, forms, price changes and engagement, with branching based on customer attributes and behavior. It supports email, SMS and push within flows. Klaviyo AU Klaviyo Help Center

It's particularly good for:

Viewed product → abandoned browse → abandoned cart → purchase → post-purchase → replenishment → winback

4. Twilio Segment Engage — best if your data is complicated

twilio.com

This becomes attractive if you have lots of behavioral data coming from your website, app, backend, CRM, warehouse, etc.

Segment can build real-time audiences from behavioral and historical data and trigger personalized journeys across email and SMS. Twilio Twilio

It's especially compelling if you already use Segment/Twilio.

What I'd choose

For a SaaS/web application:
→ Customer.io

For ecommerce:
→ Klaviyo

For a large company with sophisticated lifecycle marketing:
→ Braze

For a technically sophisticated data stack:
→ Segment Engage

One important distinction: don't choose based primarily on email template quality. Your critical requirement is the quality of the event → identity → segmentation → journey → channel pipeline. That's what determines whether you can actually build sophisticated behavior-triggered campaigns.

If you tell me what your site does, roughly how many users you have, and whether you're B2B/SaaS or ecommerce, I can narrow this to the best 2–3 options and compare pricing, implementation difficulty, APIs, event tracking, and SMS costs.

If your core requirement is “user does X on my website → send a personalized email/SMS based on that behavior,” I’d shortlist these:

My recommendation

For a SaaS website: I'd start with Customer.io.

You can track events such as:

• signed_up
• viewed_pricing
• started_trial
• invited_teammate
• created_project
• used_feature
• abandoned_checkout
• trial_ending

…and build something like:

User views pricing → wait 2 hours → if they haven't signed up → personalized email → if still inactive → SMS → if they return to pricing → change the message.

That's the type of event-driven lifecycle automation Customer.io is particularly well suited for.

For ecommerce: I'd pick Klaviyo. Its flows can trigger from events such as product views, checkout, purchases and forms, with branching based on customer attributes and behavior. It supports email and SMS in the same automated customer journeys. Klaviyo Klaviyo Help Center

For a large product/company: I'd look seriously at Braze. It supports real-time behavioral triggers across email, SMS/RCS, push, in-app and other channels, with sophisticated segmentation and journey orchestration. Braze Braze

The important distinction

Don't choose based primarily on email features. For what you're describing, I'd evaluate:

1. Event tracking — how easily can you send arbitrary events from your website/backend?
2. Identity resolution — can anonymous visitors become known users without losing their behavioral history?
3. Journey builder — can you create complex if/then, wait, branch and goal conditions?
4. Personalization — can the message contain data from the triggering event?
5. Email + SMS orchestration — can the system decide whether to email, text, or do nothing?
6. Deliverability — particularly important once you're sending at scale.
7. Pricing based on active users/events/messages — this can make a huge difference.

Klaviyo, for example, explicitly supports using event metadata to personalize triggered messages—for example, putting the actual product someone viewed or abandoned into the message. Klaviyo Help Center

If you tell me what kind of site you have (SaaS, ecommerce, marketplace, lead-gen, etc.), monthly active users, and roughly how many emails/SMS you expect to send, I can narrow this to the 2–3 best options and compare their likely cost and implementation effort.

The important distinction

Don't choose based primarily on email features. For what you're describing, I'd evaluate:

If your core requirement is “a user does X on my website → automatically send a personalized email and/or SMS”, I’d shortlist these:

*SMS availability/features depend on plan and region.

My recommendation: Customer.io

customer.io is probably the closest match if you're building a behavior-driven lifecycle system.

You can send events such as:

• signed_up
• viewed_pricing
• started_trial
• completed_onboarding
• invited_teammate
• abandoned_checkout
• subscription_upgraded

…and use those events to branch a journey.

For example:

User visits pricing → doesn't purchase → 2 hours later → personalized email → if still inactive → SMS next day → if purchases → stop journey.

Customer.io is particularly strong when your engineering/product team can send it clean event data. Current comparisons also consistently position it as a developer-friendly, event-driven lifecycle platform. Learn Hub Taqtics

When I'd choose something else

Choose Klaviyo if you're primarily ecommerce. Its strength is customer/product/purchase behavior and revenue-oriented email + SMS flows. Attentive

klaviyo.com

Choose Braze if you're a large consumer product with millions of users and want sophisticated orchestration across email, SMS, push, in-app, web, etc. It's powerful, but likely overkill for a smaller company. Braze

braze.com

Choose Iterable if you have a substantial marketing organization and want sophisticated cross-channel journey management without necessarily going all the way to Braze. Braze

iterable.com

The important distinction

I'd avoid choosing based on “email marketing platform” features. What you actually need is a customer engagement/event orchestration platform.

Your stack should ideally look like:

Website/app → behavioral events → customer profile → segmentation → journey logic → Email/SMS

The critical capabilities are:

1. Real-time event ingestion
2. Identity resolution — anonymous visitor → known user
3. Fine-grained segmentation
4. Event-based journey triggers
5. Conditional branching
6. Email + SMS in the same journey
7. Frequency limits / suppression
8. Conversion tracking
9. Easy API/SDK integration
10. Ability to stop a campaign immediately when behavior changes

If you tell me what your site does (SaaS, ecommerce, marketplace, lead-gen, etc.), roughly how many users you have, and whether you already use Segment/PostHog/HubSpot/etc., I can narrow this to the best 2–3 options and compare their actual pricing and implementation effort.

Customer.io is particularly strong when your engineering/product team can send it clean event data. Current comparisons also consistently position it as a developer-friendly, event-driven lifecycle platform. Learn Hub Taqtics

When I'd choose something else

Choose Klaviyo if you're primarily ecommerce. Its strength is customer/product/purchase behavior and revenue-oriented email + SMS flows. Attentive

klaviyo.com

Choose Braze if you're a large consumer product with millions of users and want sophisticated orchestration across email, SMS, push, in-app, web, etc. It's powerful, but likely overkill for a smaller company. braze.com

braze.com

Choose Iterable if you have a substantial marketing organization and want sophisticated cross-channel journey management without necessarily going all the way to Braze. braze.com

iterable.com

The important distinction

I'd avoid choosing based on “email marketing platform” features. What you actually need is a customer engagement/event orchestration platform.

Your stack should ideally look like:

If your core requirement is “a user does X on my website → automatically send a personalized email/SMS based on that behavior,” I’d shortlist these:

My recommendation: Customer.io

For a website or SaaS product, Customer.io is probably the first one I'd evaluate.

You can define events such as:

• signed_up
• viewed_pricing
• started_trial
• invited_teammate
• created_project
• used_feature
• abandoned_checkout
• subscription_expiring

Then build journeys like:

Viewed pricing → didn't start trial → wait 2 hours → personalized email → wait 2 days → SMS → stop if trial starts

Customer.io supports event-triggered automations based on activity on your website/app, including things like viewing a page, abandoning a cart, or completing an order. It also lets you use event properties and profile attributes for targeting. Customer.io Customer.io

That's particularly useful if you want your own product events to be the source of truth, rather than relying primarily on ecommerce events.

When I'd choose Klaviyo instead

If you're running an ecommerce business, I'd probably choose Klaviyo.

Its flows can respond to things like product views, checkout, purchases, forms, price changes, and engagement, with branching based on customer characteristics and behavior. Email and SMS can be combined in the same flow. Klaviyo Help Center Klaviyo DE

For example:

Viewed running shoes → no purchase → 4 hours → email featuring those shoes → 24 hours → SMS → purchase → exit campaign

When Braze makes sense

I'd look at Braze if you're building a fairly large consumer product/app and need sophisticated cross-channel orchestration. Its SMS platform supports real-time behavioral triggers, personalization, segmentation, experimentation, and SMS/RCS alongside other channels. Braze

It's excellent, but I'd generally not start with Braze unless you have the scale or complexity to justify it.

If you tell me what kind of site you have (SaaS, ecommerce, marketplace, lead-gen, etc.), your approximate monthly active users, and whether you need SMS in the US only or internationally, I can narrow this down to 2–3 options and compare pricing, implementation effort, APIs, and personalization capabilities.

If your core requirement is “a user does something on my website → automatically send a personalized email/SMS based on that behavior,” I’d shortlist these:

1. Customer.io — my default recommendation

This is probably the one I'd look at first if you're running a SaaS, marketplace, or web app.

You send Customer.io your users' profile data + behavioral events, then build automated journeys around them. It supports email, SMS, push, in-app/web messaging, Slack, and webhooks. Customer.io

For example:

User signs up
    ↓
Doesn't complete onboarding within 1 hour
    ↓
Email: "Need help getting started?"
    ↓
Still inactive after 24 hours
    ↓
SMS: "Hey Sarah — want a hand finishing setup?"
    ↓
User completes onboarding
    ↓
Stop campaign

The big advantage is that it's designed around events, rather than treating your audience as static email lists.

2. Klaviyo — especially if you're e-commerce

Klaviyo is excellent if your behaviors look like:

• Viewed product
• Added to cart
• Started checkout
• Purchased
• Didn't purchase
• Returned to site
• Became a VIP
• Haven't purchased in 90 days

Its flows can respond to real-time customer behavior and combine email, SMS and push in the same automation. Klaviyo Klaviyo Help Center

It also supports event data for highly personalized messages—for example, dynamically putting the exact product someone viewed or abandoned into an email/SMS. Klaviyo Help Center

I'd choose Klaviyo over Customer.io for a Shopify/DTC business.

3. Braze — if you're building something big

Braze is the heavyweight option. It supports email, SMS/RCS, push, in-app/web messaging and sophisticated cross-channel orchestration. Its journeys can react to real-time customer behavior and optimize channel selection and timing. Braze Braze

It's fantastic, but I'd generally not start with Braze unless you have the scale/team/budget to justify it.

What I'd choose

SaaS / web app: → Customer.io

E-commerce: → Klaviyo

Large consumer app / enterprise: → Braze

CRM + sales team + marketing automation: → HubSpot

One particularly important consideration: don't choose based solely on the email editor. For your use case, the quality of the event tracking, segmentation, journey builder, API, and ability to stop/re-route a campaign when behavior changes matters much more.

If you tell me roughly (1) B2B SaaS vs e-commerce, (2) monthly active users, and (3) whether you need SMS in the US, I can narrow this to the best 1–2 options and compare pricing, implementation effort, APIs, and personalization capabilities.

If your main requirement is “a user does X on my website → automatically send a personalized email/SMS based on that behavior,” I’d shortlist these:

1. customer.io — my top pick for SaaS

This is probably where I'd start if you're building a web application rather than an online store.

You can send events such as:

• signed_up
• viewed_pricing
• created_project
• invited_teammate
• used_feature_X
• abandoned_checkout

and use those events to trigger automated journeys. Customer.io specifically supports event-triggered automations based on website/app behavior, with filters based on event properties. Customer.io

Example:

User visits pricing → doesn't purchase → wait 2 hours → personalized email → wait 2 days → SMS → stop sequence if they purchase.

The big advantage is that it feels designed around product events and lifecycle messaging, rather than just traditional email marketing.

2. klaviyo.com — best for e-commerce

Klaviyo is extremely good if your behavioral events revolve around shopping:

Viewed product → abandoned cart → purchased → bought X → hasn't purchased in 60 days

Its flows can respond to real-time customer behavior and combine email, SMS and push in one workflow. Klaviyo

It also lets you insert event-specific data into messages—for example, the actual product someone viewed or abandoned. Klaviyo Help Center

I'd choose Klaviyo over Customer.io for a Shopify/DTC-type business.

3. braze.com — best if you're going big

Braze is the heavyweight option. It supports real-time behavioral triggers, sophisticated journey orchestration, personalization, experimentation, and email/SMS/RCS/push/in-app/web messaging. Braze Braze

It's particularly compelling when you eventually want logic like:

If user is high-value and viewed pricing twice and hasn't purchased → send email.
If they don't engage → SMS.
If they're active in the app → show an in-app message instead.
Dynamically choose the channel/time/content based on predicted behavior.

The downside is that it's generally more platform than a small team needs.

4. iterable.com — excellent middle/enterprise option

Iterable's Journeys can react to website/app actions, personalize based on user behavior, and send email, SMS, push, in-app and other messages. Iterable Support Center Iterable Support Center

It's worth evaluating alongside Braze if you have a serious lifecycle/marketing team.

What I'd choose

For a SaaS/web app:
🥇 Customer.io

For e-commerce:
🥇 Klaviyo

For a large consumer product with millions of users / sophisticated omnichannel journeys:
🥇 Braze

For CRM + sales + marketing all in one:
🥇 HubSpot

One important distinction: don't choose based primarily on the email editor. For your use case, the critical capability is the event/data model—how easily you can send arbitrary events from your site, attach properties to those events, identify users across anonymous → known states, and build branching journeys around them.

If you tell me what kind of site you have (SaaS, e-commerce, marketplace, media, etc.) and roughly how many users/emails per month, I can narrow this to 2–3 options and compare pricing, implementation effort, APIs, SMS costs, and personalization capabilities.

If your core requirement is “when a user does X on my site, send them a personalized email/SMS based on that behavior,” I’d shortlist these:

🥇 My pick: Customer.io

For the specific use case you described, Customer.io is probably the first product I'd evaluate.

You can send your site's events—e.g.:

• Viewed pricing page
• Started signup
• Completed step 2
• Abandoned checkout
• Used feature X
• Hasn't logged in for 14 days

…and use those events to trigger workflows. Customer.io supports email + SMS + push + in-app/web messaging in the same journey, with branching, delays, event-based triggers, segmentation, and personalization. Customer.io Customer.io

It also lets you personalize messages from user attributes and event data, including Liquid templates. Customer.io

For example:

User views your enterprise pricing page → wait 30 minutes → email personalized around the plan they viewed → if they don't respond, SMS the next day → stop the sequence if they book a demo.

That's exactly the kind of workflow Customer.io is designed for.

When I'd choose Klaviyo instead

If you're ecommerce, I'd probably pick Klaviyo.

Its flows can respond to customer actions and combine email, SMS, and push, with lots of prebuilt ecommerce workflows and integrations. Klaviyo Klaviyo

So:

Shopify/DTC/ecommerce → Klaviyo
SaaS/product with custom behavioral events → Customer.io

When I'd choose Braze

If you're building something substantial with millions of users and sophisticated cross-channel lifecycle marketing, Braze becomes very compelling. It supports real-time behavioral triggers, email, SMS, push, in-app/web messaging, experimentation, and AI-driven journey optimization. Braze Braze

But it's generally more platform than a smaller team needs.

One important architectural point

Don't choose based primarily on the email editor. For your use case, I'd evaluate how easily the platform ingests and acts on behavioral events.

Your stack ideally looks like:

Your website
    ↓
User behavior/events
    ↓
Customer.io / Klaviyo / Braze
    ↓
Segmentation + workflow logic
    ↓
Email / SMS
    ↓
User action
    ↓
New event → workflow adjusts

The really powerful part is the feedback loop: the system knows what the user did after receiving the message and can change the next message accordingly.

If you tell me whether this is SaaS, ecommerce, marketplace, or something else—and roughly how many users/month—I can narrow this to the best 2–3 options and compare pricing, implementation difficulty, APIs, and SMS costs.

If your core requirement is “a user does X on my website → send them a personalized email/SMS based on that behavior”, I’d shortlist these:

My recommendation

For a SaaS/product website, I'd start with Customer.io.

You can instrument events such as:

signed_up
created_project
invited_teammate
viewed_pricing
started_checkout
completed_purchase
inactive_7_days

Then create journeys like:

User views pricing
       ↓
Wait 30 minutes
       ↓
Did they start checkout?
   ↙          ↘
 No            Yes
 ↓              ↓
Email           Wait
 ↓              ↓
Wait 1 day      Purchase?
 ↓              ↙    ↘
SMS            No     Yes
                ↓       ↓
             Email    Exit

The important distinction is that you want a customer engagement / lifecycle automation platform, rather than a conventional email marketing tool. The platform should ingest behavioral events in real time, maintain a user profile, segment users, and orchestrate email + SMS based on what happens next.

When I'd choose each

Klaviyo — choose this if you're selling products online or want the quickest path from website behavior → polished email/SMS flows. Its flows can trigger from customer actions and event data, and it supports email, SMS and other channels. Klaviyo Help Center Klaviyo Help Center

Customer.io — my pick for a SaaS/product-led app where events like created_project, used_feature, invited_user, etc. are the center of your lifecycle strategy. It is particularly well suited to event-driven messaging.

Braze — choose this when you're operating at significant scale and need sophisticated real-time orchestration, experimentation, personalization, and multiple channels. Braze supports real-time behavioral triggers across email, SMS, push, in-app and web messaging. Braze Braze

Iterable — worth considering if you're somewhere between Customer.io and Braze in terms of organizational/marketing complexity.

Twilio — I'd choose this when your engineering team wants to own the orchestration logic and use Twilio primarily as the communications infrastructure rather than adopting a full marketing automation platform.

The one I'd pick based on your description

If you tell me what your website/app does, roughly how many users you have, and whether this is B2B SaaS, B2C, or e-commerce, I can narrow this down to 2–3 platforms and compare pricing, event tracking, personalization, SMS, APIs, and ease of implementation for your specific setup.

If your core requirement is “user does X on my website → send a personalized email/SMS → branch based on what they do next,” I’d shortlist these:

My recommendation

For a SaaS or web app: start with Customer.io.

You can send events such as:

user_signed_up
viewed_pricing
started_trial
used_feature_x
invited_teammate
abandoned_checkout
subscription_cancelled

and build logic like:

Viewed pricing
    ↓
Wait 2 hours
    ↓
Didn't start trial?
    ↓
Email personalized to their plan
    ↓
Wait 1 day
    ↓
Still hasn't started trial?
    ↓
SMS

That's exactly the type of behavior-triggered lifecycle messaging these platforms are designed around.

Klaviyo is particularly strong if you're e-commerce-focused. Its flows can trigger from events such as product views, checkout, purchases, and other tracked behavior, and it supports email + SMS in the same flow. Klaviyo Klaviyo Help Center

Braze is the one I'd investigate if you're building a sophisticated consumer product with lots of behavioral data. It supports real-time behavioral triggers, dynamic personalization, email, SMS/RCS, and cross-channel journeys. Braze Braze

Iterable is another strong enterprise choice; its journeys can react to website/app actions and user-property changes, while supporting email, SMS, push, in-app, and web push. support.iterable.com iterable.com

One important distinction

I'd separate “messaging platform” from “analytics/CDP.”

If your website already has a good event system, you can send events directly into Customer.io/Klaviyo/Braze. If your event data is scattered across your app, website, Stripe, CRM, etc., you may want something like Segment in front of the messaging platform.

If you tell me (1) SaaS vs e-commerce, (2) roughly how many users/month, and (3) whether you need SMS in the US only or internationally, I can narrow this down to the 2–3 best choices and compare pricing, implementation effort, personalization, and APIs.

If your core requirement is “user does X on my website → send a personalized email/SMS based on that behavior”, I’d shortlist these:

🥇 My pick: Customer.io

For a typical SaaS/product website, I'd start with Customer.io.

You can instrument events such as:

user_signed_up
viewed_pricing
started_trial
invited_teammate
created_project
visited_pricing_3_times
abandoned_checkout

Then build logic like:

User views pricing
        ↓
Wait 30 minutes
        ↓
Hasn't purchased?
        ↓
Send personalized email
        ↓
Wait 1 day
        ↓
Still hasn't purchased?
        ↓
Send SMS

The big advantage is that Customer.io is designed around event-driven lifecycle messaging, rather than just traditional email campaigns. It supports email, SMS, push and in-app messaging, with fairly flexible behavioral segmentation. G2 Learning Hub Vero

When I'd choose the others

Braze — choose this if you're building a serious, high-scale B2C engagement stack. It has particularly strong real-time orchestration across email, SMS, push, in-app and other channels, but it's substantially more enterprise-oriented. Braze Vero

Klaviyo — choose this if you're an ecommerce business. Its strength is connecting customer behavior to ecommerce events such as product views, carts and purchases, particularly with Shopify. Propel

Iterable — a strong middle ground for a marketing team that wants sophisticated visual journeys without going all the way into the enterprise complexity of Braze. It supports email, SMS, push and in-app messaging. Braze

What I'd use for different businesses

• SaaS / web app: Customer.io
• Startup with technical/product team: Customer.io
• Shopify / ecommerce: Klaviyo
• Large consumer app: Braze
• Large marketing team: Braze or Iterable
• SMB wanting CRM + automation: ActiveCampaign

One important distinction: don't choose based primarily on email template quality. For your use case, I'd evaluate the platforms on their event ingestion, identity resolution, segmentation, journey branching, real-time triggers, SMS integration, suppression rules, and analytics. That's what determines whether “personalized based on behavior” actually works.

If you tell me what your site does, roughly how many monthly active users you have, and whether you're B2B SaaS, B2C, or ecommerce, I can narrow this to the best 2–3 options and compare pricing + implementation complexity.

user_signed_up
viewed_pricing
started_trial
invited_teammate
created_project
visited_pricing_3_times
abandoned_checkout

Then build logic like:

User views pricing
        ↓
Wait 30 minutes
        ↓
Hasn't purchased?
        ↓
Send personalized email
        ↓
Wait 1 day
        ↓
Still hasn't purchased?
        ↓
Send SMS

The big advantage is that Customer.io is designed around event-driven lifecycle messaging, rather than just traditional email campaigns. It supports email, SMS, push and in-app messaging, with fairly flexible behavioral segmentation. learn.g2.com getvero.com

When I'd choose the others

Braze — choose this if you're building a serious, high-scale B2C engagement stack. It has particularly strong real-time orchestration across email, SMS, push, in-app and other channels, but it's substantially more enterprise-oriented. braze.com getvero.com

Klaviyo — choose this if you're an ecommerce business. Its strength is connecting customer behavior to ecommerce events such as product views, carts and purchases, particularly with Shopify.

If your core requirement is “a user does X on my website → send a personalized email/SMS → react differently based on what they do next,” I’d shortlist these:

1. customer.io — my pick for most SaaS sites

This is probably where I'd start if you're building a SaaS, marketplace, subscription product, or other behavior-driven website.

You can trigger journeys from events happening on your site/app, use event properties to personalize messages, add filters/exit conditions, and allow users to enter journeys repeatedly according to frequency rules. Customer.io Customer.io

For example:

User visits /pricing → waits 30 min → email
→ if they return to pricing → SMS
→ if they start checkout → stop campaign
→ if they purchase → send onboarding sequence

That's exactly the kind of workflow Customer.io is designed around.

2. klaviyo.com — best for ecommerce

Klaviyo is particularly strong if your behavioral events are things like:

• Viewed product
• Added to cart
• Started checkout
• Purchased
• Browsed a category
• Became inactive
• Hit a particular customer/LTV segment

Its Flows can combine email, SMS and push with branching logic based on customer behavior and attributes. Klaviyo Help Center Klaviyo

So for an ecommerce site, I'd probably choose Klaviyo over Customer.io.

3. braze.com — best if you're scaling big

Braze is the heavyweight option. It supports email, SMS/RCS, push, in-app/web messaging and other channels, with real-time behavioral orchestration and sophisticated personalization. Braze Braze

I'd consider it when you have:

• Millions of users
• Multiple products/platforms
• Complex customer journeys
• Mobile apps in addition to web
• A dedicated lifecycle/CRM team
• Significant experimentation requirements

It's probably overkill for an early-stage product.

My recommendation

If you tell me nothing else about your business: start with Customer.io.

I'd rank them:

1. Customer.io — best general-purpose behavioral messaging
2. Klaviyo — best ecommerce
3. Braze — best enterprise
4. Iterable — strong enterprise alternative
5. Twilio + Segment — best if your engineering team wants maximum control

The important distinction is that you probably don't just want an email marketing platform. You want a customer engagement/event automation platform that treats your site's events as first-class inputs.

If you tell me what your site does, roughly how many users you have, and whether you're B2B SaaS, ecommerce, marketplace, etc., I can narrow this down to the 2–3 best choices and compare pricing, implementation effort, event tracking, personalization, and SMS capabilities.

If your goal is “user does X on my site → automatically send a personalized email/SMS”, I’d shortlist these:

🥇 My recommendation: Customer.io

For a typical website/SaaS product, Customer.io is probably the one I'd start with.

You can send an event such as:

user_signed_up
pricing_page_viewed
project_created
invited_teammate
subscription_started
checkout_abandoned

and use that event to enter a workflow. Customer.io supports event-triggered automations based on activity in your website/app, filters those events using their properties, and lets you personalize messages with user/event data. Customer.io Customer.io

So you can build something like:

Viewed pricing page
        ↓
Wait 2 hours
        ↓
Did they start checkout?
   ↙           ↘
 No             Yes
 ↓               ↓
Email           Wait
 ↓               ↓
Wait 1 day      SMS
 ↓
Did they return?
 ↙        ↘
No         Yes
↓           ↓
SMS       Stop campaign

That's much closer to a behavioral messaging engine than a traditional email marketing tool.

🥈 Klaviyo if you're ecommerce

If you're selling physical products, I'd probably choose Klaviyo instead.

Its flows can trigger from things like product views, checkout starts, purchases, forms, inactivity, etc., with branching based on customer behavior. Email, SMS, and push can be combined within flows. Klaviyo Klaviyo Docs

It's particularly good for:

• Browse abandonment
• Cart abandonment
• Post-purchase sequences
• Win-back campaigns
• Product recommendations
• Email + SMS campaigns
• Customer segmentation

🥉 Braze if you're building something big

braze.com becomes interesting when you have a large user base and want sophisticated orchestration across email, SMS, push, in-app messages, etc. It's powerful, but I'd generally consider it overkill for an early-stage company.

The key distinction

I'd choose based on what your website actually is:

• SaaS / web app: Customer.io
• Ecommerce: Klaviyo
• Large consumer app: Braze
• Enterprise marketing organization: Iterable or Braze
• Developer-first + push notifications: OneSignal

One important consideration: SMS requires proper user consent, separate from email consent in many circumstances. Klaviyo, for example, explicitly requires SMS consent and provides separate compliance controls. help.klaviyo.com

If you tell me what your site does, roughly how many users you have, and what events you want to trigger messages from, I can narrow this down to the best 1–2 options and compare pricing + implementation effort + API/event tracking.

Viewed pricing page
        ↓
Wait 2 hours
        ↓
Did they start checkout?
   ↙           ↘
 No             Yes
 ↓               ↓
Email           Wait
 ↓               ↓
Wait 1 day      SMS
 ↓
Did they return?
 ↙        ↘
No         Yes
↓           ↓
SMS       Stop campaign

That's much closer to a behavioral messaging engine than a traditional email marketing tool.

🥈 Klaviyo if you're ecommerce

If you're selling physical products, I'd probably choose Klaviyo instead.

Its flows can trigger from things like product views, checkout starts, purchases, forms, inactivity, etc., with branching based on customer behavior. Email, SMS, and push can be combined within flows.

It's particularly good for:

If your core requirement is “a user does something on my website → send a personalized email/SMS based on that behavior,” I’d shortlist these:

My recommendation: Customer.io vs. Klaviyo

Choose Customer.io if you're building a SaaS, marketplace, app, or custom web product.

It's particularly well suited to events such as:

• signed_up
• created_project
• viewed_pricing
• invited_teammate
• started_checkout
• used_feature
• inactive_7_days
• subscription_expiring

You can then build logic like:

User views pricing → wait 2 hours → if they haven't started checkout → email → wait 1 day → if still inactive → SMS.

That's the type of event-driven lifecycle messaging I'd prioritize for a custom website.

Choose Klaviyo if you're e-commerce. Its Flows are explicitly designed around behavioral events, with triggers such as viewed product, started checkout, placed order, form submission and price drops. It supports email and SMS in the same flow and lets you branch based on customer behavior and attributes. Klaviyo Klaviyo Help Center

Klaviyo also supports using the actual event data in messages—for example, taking the product someone viewed or abandoned and dynamically inserting its details into an email/SMS. Klaviyo Help Center

Where I'd rank them

For a SaaS/custom website:

1. Customer.io — best fit
2. Braze — if you have a large budget/team
3. Iterable
4. Klaviyo
5. HubSpot

For e-commerce:

1. Klaviyo — best fit
2. Customer.io
3. Braze
4. Iterable
5. HubSpot

The biggest distinction is that Klaviyo is optimized around customer/e-commerce marketing data, whereas Customer.io is a particularly natural fit when your own application generates lots of custom behavioral events.

If you tell me what your site does, roughly how many users you have, and whether it's SaaS/e-commerce/lead-gen, I can narrow this down to the 2 best choices and compare pricing, implementation effort, APIs, segmentation, and SMS costs.

Choose Klaviyo if you're e-commerce. Its Flows are explicitly designed around behavioral events, with triggers such as viewed product, started checkout, placed order, form submission and price drops. It supports email and SMS in the same flow and lets you branch based on customer behavior and attributes.

If your core requirement is “a user does X on my website → automatically send a personalized email/SMS based on that behavior,” I’d shortlist these:

1. Customer.io — my default recommendation

Customer.io is particularly well suited if your site is a SaaS/product/web app rather than a traditional online store.

You can send events such as:

• signed_up
• created_project
• viewed_pricing
• invited_teammate
• used_feature
• started_checkout
• subscription_expired

…and use those events to branch users into personalized journeys. Customer.io supports event, segment, form, date, and webhook triggers, plus email, SMS, push, and in-app messaging. customer.io

It also has webhooks that can start automations from arbitrary JSON, which is useful if you have a custom backend/event pipeline. docs.customer.io

Example:

User visits pricing page → doesn't sign up → 2 hours later email → if they return to pricing → SMS → if they sign up → stop the campaign.

That's exactly the kind of workflow Customer.io is built around.

2. Braze — best if you're scaling

Braze is the more heavyweight choice. It has extremely sophisticated real-time behavioral triggers, segmentation, journey orchestration, experimentation, and cross-channel messaging. Email and SMS can both respond to real-time customer behavior. customer.iowww.braze.comdocs.customer.io

I'd choose it if you're expecting millions of users, many channels, sophisticated personalization, or a dedicated lifecycle/CRM team.

For a small startup, though, it may be more platform than you need.

3. Klaviyo — best for e-commerce

If you're selling physical products, Klaviyo jumps way up the list. Its sweet spot is behavior like:

Viewed product → abandoned cart → purchased → repeat purchase → VIP customer

For a SaaS product, I'd generally prefer Customer.io.

4. Iterable

Iterable is another strong enterprise/mid-market option for sophisticated lifecycle marketing, particularly if marketing—not engineering—is going to own the automation system.

What I'd pick

For a SaaS/web application:
🥇 Customer.io

For e-commerce:
🥇 Klaviyo

For a large consumer product with complex lifecycle orchestration:
🥇 Braze

The important thing isn't just the email/SMS editor. Make sure the platform can ingest your site's behavioral events in real time and use those events as conditions throughout a journey. Customer.io, for example, explicitly models profiles, events, segments, and automated workflows around real-time product data. docs.customer.io

If you tell me what your website/product does, roughly how many users you have, and whether you're B2B SaaS, B2C, or e-commerce, I can narrow this to the best 1–2 options and compare pricing/integration complexity.

If your core requirement is “a user does X on my website → send them a personalized email/SMS sequence”, I’d shortlist these:

My #1: Customer.io

customer.io

For what you described, Customer.io is probably the first one I'd evaluate.

You can send events from your site/product such as:

• signed_up
• viewed_pricing
• started_trial
• invited_teammate
• created_project
• used_feature
• abandoned_checkout
• subscription_expiring

…and use those events to enter users into multi-step journeys. Customer.io supports real-time event triggers, branching logic, delays, personalization, and email/SMS in the same workflow. Customer.io Customer.io Customer.io

For example:

User views pricing →

1. Wait 30 minutes
2. If they haven't signed up → personalized email
3. Wait 1 day
4. If still inactive → SMS
5. If they sign up → stop the sequence
6. If they return to pricing → send a different message
7. If they become highly engaged → notify sales

That's exactly the sort of workflow Customer.io is designed around.

When I'd choose Braze instead

braze.com

Choose Braze if you're building a substantial lifecycle/engagement operation and expect sophisticated cross-channel personalization.

Braze can react to real-time behavior and coordinate email, SMS/RCS, push, in-app, web messaging, and other channels. It also has more advanced experimentation and AI-driven decisioning. Braze Braze Braze

I'd generally think:

Customer.io → startup / SaaS / product-led growth

Braze → larger company / sophisticated consumer engagement

When I'd choose Klaviyo

klaviyo.com

If this is an ecommerce site, I'd strongly consider Klaviyo instead. It's particularly good when your behavioral data revolves around products, carts, purchases, browsing, customer profiles, and ecommerce revenue.

What I'd pick by scenario

• SaaS / web app: Customer.io
• Startup doing lifecycle marketing: Customer.io
• Ecommerce / Shopify: Klaviyo
• Large consumer app: Braze
• Enterprise omnichannel: Braze or Iterable
• CRM + marketing automation: ActiveCampaign
• Very sophisticated, high-volume behavioral messaging: Braze

One important distinction: don't optimize primarily for “email marketing.” What you want is a customer engagement/event-triggering platform that treats your site's behavioral events as first-class data. That's what makes sequences like viewed_pricing → didn't signup → returned → purchased practical rather than trying to bolt automation onto a traditional newsletter platform.

If you tell me what your site does, roughly how many users you have, and whether you're B2B SaaS/ecommerce/B2C, I can narrow this to the best 2–3 options and compare pricing, implementation effort, event tracking, and SMS costs.

I'd generally think:

Customer.io → startup / SaaS / product-led growth

Braze → larger company / sophisticated consumer engagement

When I'd choose Klaviyo

For behavior-triggered personalized email + SMS, I’d shortlist these:

🥇 My default recommendation: Customer.io

If you're building something like:

User visits pricing page → doesn't sign up → 2 hours later personalized email → if they click but don't convert → SMS next day → if they purchase → stop the campaign

Customer.io is exceptionally well suited to this. Its Journeys product can trigger workflows from customer events and branch logic across email, SMS, push, and in-app messaging in real time. customer.io

You can send events such as:

• Viewed Pricing
• Signed Up
• Started Trial
• Invited Teammate
• Used Feature X
• Abandoned Checkout
• Purchased
• Subscription Cancelled

…and use those events to drive the messaging logic.

🥈 Braze if you're serious about scale

Braze is probably the more powerful choice if you're building a sophisticated customer-engagement operation. It supports real-time behavioral triggers, email + SMS/RCS, segmentation, cross-channel orchestration, experimentation, and AI-driven optimization. www.braze.com

It can also incorporate website behavior, including real-time triggers from actions such as purchases and abandoned carts. www.braze.com

The tradeoff is that Braze generally makes more sense when you have the budget, volume, and marketing complexity to justify an enterprise-grade platform.

🛒 If you're ecommerce: Klaviyo

If your use case is Shopify/ecommerce—browse → abandon cart → purchase → replenishment → winback—I'd put Klaviyo at the top.

What I'd choose

SaaS / web app: Customer.io
Ecommerce: Klaviyo
Large company / millions of users / complex omnichannel: Braze
Mid-market marketing team: Iterable

One important distinction: I'd specifically look for a platform with a first-class event model, rather than a traditional email marketing tool with some automation bolted on. Your architecture should be able to ingest arbitrary product events and use them immediately in journey logic.

If you tell me what kind of site you have (SaaS, ecommerce, marketplace, etc.), monthly active users, and roughly how many emails/SMS you'll send, I can narrow this to the best 2–3 options and compare pricing, event tracking, API quality, personalization, SMS, and ease of implementation.

If your core requirement is “user does X on my website → send a personalized email/SMS based on that behavior”, I’d shortlist these:

My recommendation: Customer.io

For a website/product where you have events such as:

• signed_up
• viewed_pricing
• started_checkout
• created_project
• invited_teammate
• used_feature_X
• subscription_expiring

Customer.io is probably the first one I'd evaluate. It is specifically designed around real-time behavioral data, segmentation, and multi-channel messaging, including SMS, push, and in-app. customer.io

You can build flows like:

User visits pricing page
        ↓
Wait 30 minutes
        ↓
Did they start checkout?
   ↙             ↘
 YES              NO
  ↓                ↓
Don't message     Email
                   ↓
              Wait 24 hours
                   ↓
              Still inactive?
                   ↓
                  SMS

And personalize the messages using the user's attributes and behavior.

When I'd choose the others

Braze — choose this if you're already at significant scale or need sophisticated orchestration across email, SMS, push, in-app, WhatsApp, etc. It can trigger journeys from real-time customer behavior and optimize channel/timing/content. www.braze.com

Klaviyo — my pick if you're an ecommerce business. Its strength is tying browsing, carts, purchases, products, and customer profiles together for email/SMS revenue automation. maestra.io

Iterable — worth considering if you're a larger marketing organization that wants visual journey building, experimentation, segmentation, and cross-channel campaigns. www.getvero.com

ActiveCampaign — attractive when you want marketing automation plus a conventional CRM rather than a deeply product-event-oriented lifecycle platform.

The important distinction

I'd avoid choosing based primarily on “email marketing” features. What you really want is a customer engagement/event automation platform.

The architecture should look roughly like:

Your website → event tracking → customer profile/event stream → journey engine → email/SMS provider

The critical capabilities are:

1. Real-time custom events from your site/backend
2. Identity resolution — anonymous visitor → logged-in user
3. Conditional journeys
4. Event-based triggers
5. Email + SMS in the same workflow
6. Per-user personalization
7. Frequency/campaign suppression
8. Conversion attribution
9. Webhooks/API
10. Good deliverability

For a SaaS/product-led website, my ranking would be:

1. Customer.io → 2. Braze → 3. Iterable → 4. ActiveCampaign

For ecommerce, I'd switch that to:

1. Klaviyo → 2. Braze → 3. Customer.io → 4. Iterable

If you tell me what your site does, roughly how many users you have, and whether you're SaaS/ecommerce/marketplace, I can narrow this to the best 2–3 options and compare pricing, event tracking, SMS costs, integrations, and implementation difficulty.

If your goal is “user does X on my website → automatically send a personalized email/SMS → branch based on what they do next,” I’d shortlist these:

1. Customer.io — my first choice

Customer.io

This is probably the closest match to what you're describing. You can define behavioral events such as:

• signed_up
• viewed_pricing
• started_trial
• created_project
• invited_teammate
• abandoned_checkout
• subscription_cancelled

…and use those events to start automated workflows. Customer.io explicitly supports automation triggers, multi-step workflows, and transactional email/SMS. docs.customer.io

For example:

User visits pricing → doesn't sign up → 2 hours later email → clicks email → SMS next day → signs up → stop campaign.

That's exactly the sort of workflow I'd use Customer.io for.

2. Braze — best if you're serious about lifecycle messaging

Braze

Braze is substantially more sophisticated. It supports real-time behavioral triggers, personalized email, SMS/RCS, web messaging, in-app messaging, experimentation, and AI-driven journey optimization. www.braze.com

I'd pick Braze if you're expecting millions of users, many channels, complex segmentation, and a dedicated lifecycle/CRM team.

For a startup with a relatively small user base, though, it can be more platform than you need.

3. Iterable — excellent enterprise alternative

Iterable

Iterable is particularly strong for visual, cross-channel journeys. It supports behavioral personalization, real-time segmentation, email, SMS, in-app, web, and other channels. iterable.com

I'd put it roughly in the same enterprise category as Braze.

What I'd choose

If you're a SaaS/startup: → Customer.io

If you're ecommerce: → Klaviyo

If you're an established company with a large lifecycle-marketing operation: → Braze

If you already use HubSpot heavily: → HubSpot

If you're enterprise and want sophisticated cross-channel orchestration: → Iterable or Braze

The important thing is that you don't just want an email marketing tool. You want a behavioral event → customer profile → journey orchestration system.

If you tell me your website stack (e.g. React/Next.js, WordPress, Shopify), approximate monthly active users, and whether you need transactional vs. marketing SMS, I can narrow this down to the best 2–3 options and compare pricing/integration complexity.

If your core requirement is “a user does X on my website → send them a personalized email/SMS → react to what they do next,” I’d shortlist these:

🥇 My pick: Customer.io

Customer.io is particularly well suited if you're building a SaaS, marketplace, subscription product, or other product where your own application events are the source of truth.

You can send events such as:

• signed_up
• completed_onboarding
• viewed_pricing
• started_checkout
• invited_teammate
• used_feature_X
• subscription_expiring
• inactive_for_7_days

…and use those events to branch a journey. Customer.io supports real-time event triggers, behavioral conditions, branching, personalization, email, SMS, push, and in-app messaging. customer.io

For example:

User visits pricing → doesn't purchase
→ wait 2 hours
→ personalized email
→ if they return to pricing → SMS
→ if they purchase → stop campaign
→ if they don't → send a different email 3 days later.

That's exactly the kind of workflow Customer.io is designed around. customer.io

🛒 If you're e-commerce: Klaviyo

Klaviyo would probably be my first choice instead.

Its flows can trigger from website/customer actions, and it has particularly strong email + SMS automation around browsing, carts, purchases, and post-purchase behavior. help.klaviyo.com

🏢 If you're big enough for enterprise tooling

I'd look at Braze or Iterable. They're excellent for sophisticated omnichannel customer journeys, particularly at large scale, but they're generally more infrastructure and budget than a startup needs. www.getvero.com

The important distinction

I'd choose based on where your behavioral data comes from:

• Your SaaS/app's events → Customer.io
• Shopify/e-commerce behavior → Klaviyo
• Millions of consumers + mobile app + many channels → Braze
• Large/mid-market omnichannel marketing team → Iterable
• CRM/sales automation is central → HubSpot

If you tell me what your website does, roughly how many users you have, and whether you need transactional SMS as well as marketing SMS, I can narrow this down to the best 2–3 options and compare their current pricing, APIs, event tracking, and implementation effort.

If your core requirement is “a user does X on my site → automatically send a personalized email/SMS sequence”, I’d shortlist these:

My picks

1. Customer.io — best overall for a SaaS/product website

This would be my first look if you're building a software product rather than an online store. You can send events from your website/backend and use them to enter people into highly specific automated campaigns. It supports both email and SMS in the same workflow, with dynamic personalization. docs.customer.io

For example:

User signs up → doesn't complete onboarding → email after 1 day → visits pricing page → SMS 2 hours later → upgrades → immediately stop the campaign.

Customer.io is particularly good when your own product events are the source of truth.

Customer.io

2. Klaviyo — best if you're e-commerce

Klaviyo makes this kind of automation exceptionally easy. Its flows can trigger on events such as product views, checkout starts, purchases, form submissions, and inactivity, with branching based on customer attributes. Email and SMS can live in the same flow. www.klaviyo.com

Klaviyo

3. Braze — best if you're operating at significant scale

Braze is the heavyweight option. Its Canvas system can react to real-time customer behavior and orchestrate email, SMS, push, in-app, WhatsApp, and other channels. It's especially compelling if you have a mobile app or sophisticated cross-channel engagement requirements. www.braze.com

Braze

What I'd choose

• SaaS / web app: Customer.io
• E-commerce: Klaviyo
• Consumer app with millions of users / complex lifecycle marketing: Braze
• You want CRM + sales + marketing in one system: HubSpot
• Small business wanting relatively easy automation: ActiveCampaign

One important distinction: don't choose based primarily on “email automation.” For your use case, the important capability is a robust event-based customer data model—you want to be able to send events such as signup, viewed_pricing, started_trial, invited_teammate, created_project, subscription_expiring, etc., then branch journeys based on those events.

If you tell me what your site/product does, roughly how many users you have, and whether this is B2B SaaS, B2C, or e-commerce, I can narrow this down to the best 2–3 and compare pricing, implementation effort, APIs, segmentation, and SMS costs.

If your core requirement is “someone does something on my site → send a personalized email/SMS based on that behavior”, I’d shortlist these:

My pick: Customer.io

For a typical software/SaaS company, I'd start with Customer.io. Its Journeys product is explicitly built around triggering workflows from customer events and can branch across email, SMS, push, and in-app messaging. It also supports personalization at send time based on behavior, preferences, and lifecycle stage. customer.io

For example:

User signs up → doesn't complete onboarding → wait 2 days → personalized email → if they return but don't activate → SMS → if they activate → stop the campaign.

You can feed it events such as:

• signed_up
• viewed_pricing
• started_trial
• invited_teammate
• created_project
• used_feature_x
• trial_ending
• subscription_cancelled

When I'd choose the others

Klaviyo is the better choice if you're selling physical products. Its flows can trigger from things like product views, checkout, purchases, forms, inactivity, etc., and combine email and SMS in the same customer journey. www.klaviyo.com

Braze is what I'd consider when you have a larger user base and need very sophisticated cross-channel orchestration. It supports real-time behavioral triggers, dynamic personalization, segmentation, email, SMS/RCS, push, in-app and web messaging. www.braze.com

HubSpot makes sense if you want marketing automation tightly integrated with CRM, sales pipelines, forms, lead scoring, etc., rather than primarily being a behavioral messaging engine.

The architecture I'd recommend

If you're building a SaaS/product, I'd generally do:

Your website/app → event tracking → Customer.io → email/SMS

rather than trying to make your web application directly send every message.

The important part is choosing a platform that understands events, not just email lists. You want to be able to say:

IF
  user viewed pricing
  AND hasn't started trial
  AND has email consent

THEN
  wait 1 day
  send personalized email

IF
  user returns to pricing
  AND still hasn't started trial

THEN
  send SMS

Customer.io is particularly well suited to this kind of event-driven workflow. customer.io

If you tell me what kind of site you have (SaaS, ecommerce, marketplace, lead-gen, etc.), roughly how many users you have, and whether you need transactional SMS as well as marketing SMS, I can narrow this down to the best 2–3 options and compare pricing, ease of implementation, APIs, and event tracking.

For personalized email + SMS triggered by user behavior on your site, the best software depends mostly on whether you’re a SaaS product, ecommerce store, marketplace, or content business. The strongest options are event-driven customer engagement platforms rather than traditional email marketing tools. www.sequenzy.comlearn.customer.io

Best overall for product behavior triggers (SaaS / apps)

Customer.io

Best for: “User signed up → didn’t complete onboarding → send email → if they still don’t activate → send SMS → if they convert → stop campaign.”

Strengths:

• Trigger from custom events (created_account, viewed_pricing, completed_step_2, etc.)
• Advanced segmentation and branching logic
• Email, SMS, push, and in-app messaging
• Good fit for engineering teams that can send product events www.sequenzy.comlearn.customer.io

Tradeoff:

• Requires more setup than drag-and-drop marketing tools.

Best for ecommerce (Shopify / DTC)

Klaviyo

Best for: abandoned carts, browse abandonment, post-purchase flows, VIP customers, replenishment reminders.

Strengths:

• Very strong ecommerce integrations
• Email + SMS in one platform
• Revenue attribution for campaigns
• Prebuilt behavioral flows www.clickpost.ai

Tradeoff:

• Less flexible than developer-first platforms for unusual product events.

Best enterprise / high-scale consumer apps

Braze

Best for: mobile apps, marketplaces, fintech, large consumer products.

Strengths:

• Real-time behavioral campaigns
• Email, SMS, push, and in-app orchestration
• Sophisticated personalization and lifecycle journeys www.clickpost.ai

Tradeoff:

• Expensive and usually requires dedicated marketing ops resources.

Best if you want CRM + automation together

HubSpot

Best for: B2B companies where website behavior should influence sales follow-up.

Examples:

• Visited pricing page 3 times → notify sales
• Downloaded a guide → enroll in nurture
• Became a qualified lead → start SMS sequence

Tradeoff:

• Can become expensive as automation requirements grow. zapier.com

Best simpler option for smaller teams

ActiveCampaign

Best for: businesses that need automation but don’t want to build a full event pipeline.

Good for:

• Email sequences
• Lead scoring
• CRM-triggered messaging
• Basic behavioral automation www.emailservicebusiness.com

My shortlist by scenario

A typical setup I’d recommend for a modern SaaS product:

Website/app events → customer data layer → Customer.io → email/SMS journeys

Track events like:

• Signup completed
• First key action completed
• Feature used
• Pricing page viewed
• Trial ending
• Subscription canceled
• User inactive for X days

Then create journeys:

• Activation onboarding
• Trial conversion
• Feature education
• Win-back
• Expansion/upsell

If you tell me what type of business you run (SaaS, ecommerce, marketplace, etc.), your monthly active users, and whether you already have a backend/event tracking system, I can narrow this to 2–3 best fits.

If your core requirement is “user does X on my site → send a personalized email/SMS → branch based on what they do next,” I’d shortlist these:

1. Customer.io — best overall for product-led / SaaS

Customer.io

This would be my first choice for most SaaS, marketplaces, and web apps. It is built around behavioral events: page views, cart abandonment, purchases, signups, custom events, etc. You can branch journeys, use event data for personalization, and send email + SMS + push + in-app from the same workflow. customer.iodocs.customer.io

Great for:
Viewed pricing → wait 2 hours → email → if signed up, stop → otherwise SMS → if clicked, sales notification

2. Klaviyo — best for ecommerce

Klaviyo

If you're selling physical products, I'd lean toward Klaviyo. Its flows natively handle things like viewed product, started checkout, purchased, form submission, and inactivity, with email and SMS in the same automation. www.klaviyo.com

Great for: browse abandonment, abandoned cart, post-purchase, winback, promotions, product recommendations.

3. Braze — best for large-scale / sophisticated engagement

Braze

Braze is the heavyweight option. It supports real-time behavioral triggers and orchestration across email, SMS/RCS, push, in-app, web messaging, and more, with sophisticated segmentation and experimentation. www.braze.com

Great for: millions of users, mobile apps, complex customer journeys, sophisticated personalization.

My quick recommendation

For your exact wording, I'd start with Customer.io. Its model is particularly well suited to sending messages based on arbitrary events from your website rather than just traditional marketing-list behavior. You can send your own events and event properties into the platform and use them to trigger and personalize journeys. docs.customer.io

If you tell me what kind of site you have (SaaS, ecommerce, marketplace, lead-gen, etc.), monthly active users, and roughly how many emails/SMS you'll send, I can narrow this down to the best 2–3 and compare pricing, event tracking, SMS costs, APIs, and ease of implementation.

If your core requirement is “a user does X on my website → send a personalized email/SMS → branch based on what they do next,” I’d shortlist these:

My pick: Customer.io

For a typical SaaS or web app, Customer.io is probably the best fit.

It is designed around event-driven journeys: you can trigger workflows from essentially any customer event, branch on behavior, and communicate through email, SMS, push, and in-app messaging. customer.io

For example:

User signs up → doesn't complete onboarding → wait 2 days → personalized email → if they visit pricing page → SMS → if they upgrade → exit campaign

That's the kind of workflow Customer.io is particularly good at.

If you're ecommerce: Klaviyo

I'd choose Klaviyo instead if you're selling physical products or running a consumer ecommerce business. Its flows can react to events such as product views, checkout, purchases, forms, price drops, and inactivity, with email/SMS/push in the same workflow. www.klaviyo.com

It's also considerably easier to get started with than something like Braze.

If you're big: Braze

Braze is the more enterprise-oriented choice. It's particularly strong when you need sophisticated cross-channel orchestration, real-time behavioral triggers, granular segmentation, experimentation, and very large volumes. Its SMS product supports real-time triggers based on customer behavior and backend events, alongside email, push, in-app, and other channels. www.braze.com

I'd avoid starting with Braze unless you actually need that level of sophistication.

The key question

The biggest differentiator isn't really email vs. SMS—all of these can do both. It's how you get your behavioral data into the platform.

For example, you want to be able to send events such as:

user_signed_up
project_created
invited_teammate
viewed_pricing
started_checkout
subscription_started
subscription_cancelled

and attach properties:

plan = "pro"
company_size = 25
project_name = "Acme"

Then your messaging platform turns those events into personalized journeys.

My ranking for most startups:

1. 🥇 Customer.io — best overall for behavioral/product-led messaging
2. 🥈 Klaviyo — best for ecommerce
3. 🥉 Braze — best for enterprise / high-scale consumer apps
4. Iterable — excellent for sophisticated lifecycle teams
5. HubSpot — best if you also want your CRM/sales/marketing system under one roof

If you tell me what kind of site you have (SaaS, ecommerce, marketplace, media, etc.), roughly how many users you have, and whether you need transactional as well as marketing messages, I can narrow this to the 2–3 best choices and compare pricing, event tracking, APIs, deliverability, and SMS costs.

For personalized email + SMS triggered by user behavior on your site, you’re looking for a customer engagement platform (not just an email newsletter tool). The best choice depends on your business model, traffic volume, and how sophisticated your triggers need to be. www.getvero.com

Best overall options

My picks by use case

If you run SaaS / a web app

1. Customer.io — best fit for event-driven messaging
2. Braze — if you have millions of users and enterprise needs
3. Intercom — if in-app chat/help is also central

Example triggers:

• User signs up → send onboarding sequence
• User visits pricing page 3 times → send sales-assist SMS
• User starts setup but stops → send reminder
• User reaches usage threshold → send upgrade nudge

If you run ecommerce

1. Klaviyo
2. Attentive
3. Omnisend

Example triggers:

• Viewed product → SMS reminder
• Added to cart → abandoned cart flow
• Purchased → review request + cross-sell
• No purchase in 90 days → win-back campaign

If you are technical and want maximum control

• Customer.io is usually the sweet spot: send custom events from your backend, define segments, and build journeys without building the messaging infrastructure yourself. getoden.com

Features I would require

Whatever you choose, make sure it supports:

• Custom event tracking (not just page visits)
• User profiles with attributes
• Branching journeys (“if/then” logic)
• Email + SMS in the same workflow
• Frequency limits (avoid annoying users)
• A/B testing
• Webhooks/API access
• Consent management for SMS compliance
• Integration with your analytics stack (Segment, Snowflake, Amplitude, etc.) www.getvero.comgetoden.com

A common architecture looks like:

Your website/app → event tracking → customer engagement platform → personalized email/SMS

If you tell me:

1. SaaS vs ecommerce vs marketplace,
2. monthly active users/customers,
3. your tech stack (Shopify, React, WordPress, custom app, etc.), and
4. approximate monthly budget,

I can narrow this to 2–3 best choices.

If your core requirement is “when a user does X on my website, send a personalized email/SMS based on that behavior”, I’d shortlist these:

\*SMS capabilities/costs depend on configuration.

🥇 My recommendation: Customer.io

For a website where you want triggers such as:

User signs up → waits 10 minutes → hasn't completed onboarding → email

User visits pricing page 3 times → send personalized email

User starts checkout → doesn't finish → SMS after 30 minutes

User uses Feature X → send an email showing them Feature Y

User becomes inactive → start a re-engagement sequence

Customer.io is probably the strongest fit. Its Journeys product is explicitly built around real-time events, attributes, segments, webhooks, branching logic, delays, and multi-channel messaging across email and SMS. customer.iowww.klaviyo.comwww.braze.com

You can essentially feed it an event stream from your site:

user_id: 123
event: viewed_pricing
plan: pro
company: Acme
pages_viewed: 7
last_login: today

…and use those properties to determine whether to message, what to say, which channel to use, and what happens next.

Customer.io

When I'd choose the others

Klaviyo — choose this if you're primarily e-commerce. Its flows can react to things like product views, checkout starts, purchases, forms, inactivity, and other customer behaviors, with email/SMS in the same flow. www.klaviyo.com

Klaviyo

Braze — choose this if you're operating at significant scale and want sophisticated cross-channel orchestration, experimentation, mobile/app messaging, and real-time personalization. It's powerful but generally much heavier than you need for an early-stage product. www.braze.com

Braze

HubSpot — attractive when the automation needs to interact heavily with your sales CRM, leads, deals, sales reps, and B2B lifecycle rather than just product behavior.

HubSpot

One important distinction

I would not start by looking for a traditional “email marketing” tool.

What you're describing is really a customer engagement / event-driven messaging platform.

The architecture you want is roughly:

Your website → behavioral events → customer engagement platform → decision/journey engine → email/SMS

The most important question is therefore whether the platform can ingest arbitrary events from your application, not just things like “opened email” or “filled out form.”

For that reason, Customer.io would be my first demo, especially for SaaS, marketplaces, subscriptions, or other product-led websites. Its current platform specifically supports event-triggered journeys and real-time behavioral conditions. www.braze.comcustomer.io

If you tell me what your website does (SaaS, e-commerce, marketplace, lead-gen, etc.), roughly how many users you have, and whether you're using Segment/PostHog/GA4/etc., I can narrow this to the best 2–3 options and compare pricing, implementation effort, and exact architecture.

If your core requirement is “when a user does X on my site, automatically send them a personalized email/SMS based on that behavior,” I’d shortlist these:

🥇 My pick: Customer.io

For a typical SaaS or web product, I'd start with Customer.io.

It is specifically designed around behavioral/event-driven messaging. You can send events such as:

• signed_up
• viewed_pricing
• started_checkout
• created_project
• invited_teammate
• used_feature
• subscription_expiring

…and then build workflows such as:

User visits pricing → wait 30 minutes → if they haven't signed up → personalized email → if they still haven't converted → SMS → stop when they purchase.

Customer.io supports email, SMS, push and in-app messaging, with branching logic based on events, segments and user attributes. customer.io

It's also relatively accessible compared with Braze/Iterable; current comparisons put Customer.io's entry pricing around $100/month, whereas Braze and Iterable are generally sales-led enterprise products. customer.iolearn.g2.commaestra.iowww.braze.comiterable.comwww.getvero.com

When I'd choose something else

Klaviyo → If you're running Shopify/ecommerce. Its strength is customer/product/purchase behavior and email + SMS revenue flows. maestra.io

Braze → If you have a large consumer product, lots of users, mobile apps, and need sophisticated real-time orchestration across email/SMS/push/in-app. It can trigger messages directly from real-time behavioral events. www.braze.com

Iterable → If you're a larger marketing organization that wants marketers to build sophisticated cross-channel journeys without engineering involvement. iterable.com

HubSpot → If you want the behavioral automation tightly connected to sales CRM, lead management, forms, pipeline, etc. I wouldn't choose it solely for event-triggered messaging.

The architecture I'd recommend

If you're building a SaaS/product, I'd generally do:

Website/app → event tracking → Customer.io → Email/SMS

For example:

User visits pricing
        ↓
Track "pricing_viewed"
        ↓
Customer.io
        ↓
Is user already a customer?
    ↙          ↘
   yes          no
   ↓             ↓
   stop      wait 2 hours
                  ↓
             Send personalized email
                  ↓
             Did they sign up?
              ↙       ↘
            yes        no
             ↓          ↓
            stop     SMS next day

The important thing is to choose a system where events are first-class inputs, rather than merely uploading lists and scheduling campaigns. Customer.io, Braze and Iterable are particularly strong in this model. learn.g2.comwww.getvero.com

If you tell me (1) SaaS/ecommerce/marketplace, (2) roughly how many users you have, and (3) whether you need SMS in the US only or internationally, I can narrow this to the best 2–3 options and compare actual pricing, implementation difficulty, event tracking, personalization, and SMS costs.

If your main requirement is “user does X on my website → automatically send a personalized email/SMS → branch based on what they do next,” I’d shortlist these:

1. Customer.io — best overall for SaaS / product-led sites

This would be my default recommendation if you're building a software product.

• Trigger journeys from arbitrary events: signup, feature usage, pricing-page visit, trial activity, purchase, etc.
• Strong branching and multi-step workflows.
• Email + SMS + push + in-app in the same journey.
• Particularly good when your engineering team can send rich event data into the platform. customer.io
• It has a relatively accessible entry point compared with enterprise platforms. learn.g2.com

Example:
Viewed pricing → wait 2 hours → if started trial, stop → otherwise email → if email clicked but no signup, SMS next day.

2. Klaviyo — best for ecommerce

I'd choose this over Customer.io if you're selling physical products online.

Its Flows can react to real-time behavior such as product views, checkout starts, purchases, forms and inactivity, with email and SMS coordinated in one workflow. www.klaviyo.com

It's especially strong for things like:

Viewed product → abandoned cart → purchase → post-purchase → replenishment → winback

3. Braze — best for large-scale consumer apps

Braze is the heavier-duty option when you have significant user volume and want sophisticated cross-channel orchestration.

It is designed around real-time customer behavior and can coordinate email, SMS, push, in-app and other channels. learn.g2.com

The tradeoff is cost and complexity—I'd generally avoid it for an early-stage company unless you have a strong reason to go enterprise.

4. Iterable — strong mid-market/enterprise alternative

Good if you want sophisticated cross-channel journey orchestration and experimentation without necessarily going all the way to Braze. It supports email, SMS, push and in-app journeys. www.getvero.com

My quick decision tree

For your wording specifically, I'd start with Customer.io. Its model is very close to what you're describing: send arbitrary user events from your site, use those events to enter journeys, personalize the message with event/user data, and branch the journey according to subsequent behavior. customer.io

If you tell me what kind of site you have (SaaS, ecommerce, marketplace, lead-gen, etc.), monthly active users, and roughly how many emails/SMS you expect to send, I can narrow this down to the best 2–3 and compare pricing, implementation effort, event tracking, personalization, and SMS costs.