ChatGPT answers, unedited

For combining an automated email onboarding series + SMS nudges for new users, the best software depends mostly on whether you’re a SaaS/product team, ecommerce brand, or a sales-led business. The strongest options are:

My shortlist by use case

If you’re onboarding SaaS users:

1. Customer.io — best overall fit
2. Braze — if you’re at large scale
3. Intercom — if onboarding includes chat, support, and in-app education

If you’re a B2B company with sales involved:

1. HubSpot
2. Customer.io
3. ActiveCampaign

If you’re ecommerce:

1. Klaviyo
2. Omnisend
3. HubSpot

A typical high-performing onboarding setup looks like:

• Day 0: Welcome email immediately after signup
• Day 1: SMS reminder if user hasn’t completed setup
• Day 3: Feature education email based on behavior
• Day 5: Case study/social proof
• Day 7: Activation nudge or onboarding call offer
• Branches based on events:
  • Completed setup → move to adoption series
  • Stalled → send help content
  • Highly engaged → invite to upgrade/referral

For most early-to-mid-stage SaaS companies, I’d start with Customer.io because it gives you the behavioral automation depth you need without requiring an enterprise engagement stack. www.getvero.comcustomer.io

If you share your business type (SaaS, ecommerce, marketplace, etc.), user volume, and whether you need in-app messages, I can narrow it to 2–3 choices.

If your goal is specifically “new user signs up → automated email onboarding → SMS nudge if they haven’t activated”, I’d shortlist these:

🥇 My pick: Customer.io

Customer.io is particularly well suited to onboarding because its Journeys product is built around event-triggered, multi-step workflows across email, SMS, push, and in-app messaging. customer.iocustomer.io

For example:

Signup
→ Email: “Welcome — here’s how to get started”

+1 day
→ If completed_setup = false → Email: “Finish setting up your account”

+2 days
→ If still inactive → SMS: “Need a hand getting started? Here’s the 2-minute setup.”

User activates
→ Exit onboarding immediately

User doesn't activate
→ Different branch with a more educational email/SMS sequence.

Customer.io explicitly supports onboarding use cases and recommends using email for returning users to the inbox and SMS when you need a more immediate nudge. customer.io

🥈 Braze

Braze is the better choice if you're building a serious lifecycle/engagement infrastructure rather than just an onboarding sequence.

It supports coordinated email, SMS/RCS, push, in-app, behavioral triggers, segmentation, experimentation, and real-time journey orchestration. customer.iowww.braze.comcustomer.io

I'd choose Braze if you expect to eventually have flows like:

Signup → onboarding → activation → trial conversion → retention → upsell → churn prevention

with lots of behavioral branching and multiple channels.

When I'd choose HubSpot

HubSpot makes more sense if onboarding is closely tied to sales, CRM, lead management, and customer support. You get a broader business platform rather than a specialized product-engagement engine.

The important distinction

I wouldn't pick software based simply on “does it send email and SMS?”

I'd prioritize whether it can do:

1. Event-based triggers — signup, completed profile, created project, invited teammate, etc.
2. Behavioral branching — don't send the SMS if they've already activated.
3. Cross-channel orchestration — email and SMS should behave as one journey.
4. Conversion/activation tracking — measure whether onboarding actually produces activated users.
5. Easy integration with your product events.
6. SMS consent/unsubscribe management.
7. Frequency controls so users don't get bombarded.

Customer.io and Braze are particularly strong here. Customer.io supports event-triggered journeys, branching, delays, A/B testing, conversion goals, and multiple messaging channels. customer.io

Bottom line:

• Early/mid-stage SaaS: Customer.io
• Scale-up/enterprise product: Braze
• CRM-centric company: HubSpot
• Engineering-heavy/custom infrastructure: Twilio + Segment

If you tell me your number of new users/month, whether it's B2B or B2C, and your approximate budget, I can narrow this to the best 2–3 and compare pricing/features.

If your goal is “new user signs up → automated onboarding emails + behavioral SMS nudges from the same journey”, I’d shortlist these:

🥇 My pick: Customer.io

For a typical SaaS/product onboarding flow, I'd start with Customer.io. It is specifically designed around behavioral, event-triggered journeys and supports email, SMS, push, and in-app messaging in the same workflow. Customer.io Customer.io

For example, you could build:

Day 0

• Signup → welcome email
• 10 min later → if user hasn't completed setup, SMS nudge

Day 1

• Email explaining the core feature
• If they've already used it → skip the email
• If they haven't → send a different message

Day 3

• SMS: “Need a hand getting started?”
• If they've activated → stop onboarding
• Otherwise → email with a specific next step

That's exactly the sort of behavioral branching Customer.io is built for. Its onboarding tooling explicitly supports triggers based on product actions and branching so users don't receive reminders for things they've already completed. Customer.io

It also supports SMS directly in the visual workflow, including behavioral onboarding nudges, and can use Twilio or another SMS provider. Customer.io

customer.io

When I'd choose Braze instead

Choose Braze if you're already operating at substantial scale or need a much broader customer-engagement stack—email + SMS/RCS + push + in-app + WhatsApp, sophisticated experimentation, real-time decisioning, etc. Its Canvas journey builder is particularly strong for complex cross-channel orchestration. Braze Braze

braze.com

The important distinction

I wouldn't choose based primarily on email automation features. Almost all of these tools can do drip email.

I'd evaluate them on:

1. Can product events trigger the journey in real time?
2. Can email and SMS live in the same workflow?
3. Can the workflow branch based on what the user did?
4. Can it automatically stop messages once the user activates?
5. Can you measure activation/conversion rather than just email opens?
6. How painful is the integration with your product/database?
7. How does SMS consent/compliance work for your audience?

For a B2B SaaS with, say, 1k–100k new users/month, I'd generally pick Customer.io before Braze. For a large consumer app with millions of users and a sophisticated lifecycle team, I'd lean Braze.

If you tell me your product type, monthly new users, and whether you already use Segment/PostHog/HubSpot/etc., I can narrow this to the best 2–3 options and compare pricing, SMS costs, integrations, and implementation effort.

For automated onboarding that combines email sequences with SMS nudges, I’d shortlist these:

1. Customer.io — my default recommendation

Customer.io

Customer.io is particularly well suited to product onboarding. Its Journeys builder can react to product events and branch users into different paths across email, SMS, push, and in-app messaging. customer.io

For example:

Signup → Email welcome → wait 1 day → did user complete setup?
→ Yes: continue onboarding
→ No: SMS nudge
→ wait 2 days → email with tutorial
→ activated: exit onboarding

It also supports event-based triggers, delays, branching, A/B testing, conversion goals, and subscription management. customer.io

Why I'd pick it: It feels designed around the exact problem of "a user did X, so now send Y," rather than traditional newsletter marketing.

2. Braze — best if you're building a sophisticated lifecycle engine

Braze

Braze is the more powerful choice if you expect onboarding to eventually span email + SMS + push + in-app + WhatsApp/RCS, with sophisticated personalization and real-time decisioning. Its Canvas journey builder coordinates channels from one interface and can react to live customer behavior. www.braze.com

The downside is that it's generally more platform than an early-stage SaaS needs.

3. HubSpot — best if CRM is equally important

HubSpot

HubSpot's workflows can automate multi-step processes using CRM data, and its SMS product integrates SMS with workflows, personalization, consent management, and quiet hours. www.hubspot.com

I'd choose it if your onboarding is closely connected to sales, CRM, customer success, and marketing, rather than purely product activation.

My ranking

For a typical SaaS/product:

1. 🥇 Customer.io — best balance of product-event triggers, email/SMS, flexibility, and ease of building journeys.
2. 🥈 Braze — best if you're at significant scale or need sophisticated cross-channel orchestration.
3. 🥉 HubSpot — best if you want CRM + sales + marketing automation in one ecosystem.

One important design principle: don't simply duplicate the email sequence via SMS. Use email for education/context and SMS for short, time-sensitive nudges when the user hasn't completed a key activation action. Customer.io specifically positions email, SMS, in-app, and push differently during onboarding. customer.io

If you tell me your approximate new users/month, B2B vs B2C, and what the key activation event is, I can narrow this down to the best 1–2 options and estimate what the setup would look like.

For automated onboarding of new users, where you want email + SMS nudges tied to product behavior, I’d shortlist these:

🥇 My pick: Customer.io

If you're onboarding software users, rather than shoppers, I'd choose Customer.io. Its Journeys product is specifically designed for event-driven, multi-step journeys across email, SMS, push, and in-app messaging. You can branch journeys based on what the user actually does in your product. customer.io

For example:

Signup → Email immediately
→ User doesn't complete setup after 24h
→ SMS nudge
→ User completes setup
→ Email with next feature
→ User hasn't invited teammate after 3 days
→ SMS/email reminder
→ User becomes activated
→ Exit onboarding

That event-based logic is the key feature I'd prioritize over simply having "email + SMS."

🥈 Braze

Braze is the better choice if you're building a large-scale consumer product and expect sophisticated lifecycle orchestration. It supports email, SMS, push, in-app and other channels, with real-time behavioral triggers and advanced personalization. www.braze.com

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

🥉 Klaviyo

Klaviyo is excellent if your "new users" are really customers/leads/subscribers, particularly in ecommerce. Its Flows support email + SMS + branching logic, and it has lots of prebuilt automation. www.klaviyo.com

One wrinkle: Klaviyo actually recommends separate email and SMS welcome flows because users can consent to those channels independently. help.klaviyo.com

What I'd choose by situation

• B2B SaaS / app / product-led growth → Customer.io
• Consumer app with millions of users → Braze
• Shopify/ecommerce → Klaviyo
• Very simple onboarding → Klaviyo or Customer.io
• Highly behavioral onboarding with lots of product events → Customer.io
• Email + SMS + push + in-app + sophisticated experimentation → Braze

One important distinction: don't choose based primarily on email/SMS capabilities. All three can do that. Choose based on how well the platform can consume your product events (signup, completed_profile, created_project, invited_teammate, used_feature_X, etc.) and make those events control the journey. Customer.io is particularly strong for this use case. customer.io

If you tell me what kind of product you're onboarding (B2B SaaS, consumer app, marketplace, etc.), approximate monthly new users, and your tech stack, I can narrow this down to the best 2–3 and compare pricing, implementation effort, SMS costs, integrations, and onboarding UX.

If your goal is specifically “new user signs up → automated email onboarding → behavioral SMS nudges → stop/branch based on what they do”, I’d shortlist these:

🥇 My pick: Customer.io

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

It is designed around behavior-triggered customer journeys, rather than simply email newsletters. You can build a workflow like:

Signup
→ Email: “Welcome — here's how to get started”
→ Wait 1 day
→ Did user complete setup?

• Yes → Email with advanced feature
• No → SMS: “Need help getting set up?”

→ Wait 2 days
→ Did user perform key activation event?

• Yes → move to next onboarding stage
• No → Email with use case/tutorial

→ SMS reminder
→ Exit onboarding once activated

Customer.io supports email, SMS, push, in-app and other channels within the same visual workflow, with event-based triggers, branching, delays, A/B testing and conversion goals. customer.io

It also explicitly supports welcome/onboarding series and behavioral automations, and its current platform is built around real-time customer events. docs.customer.io

🥈 Braze if you're scaling

Braze is the more enterprise-grade choice.

It's particularly compelling if you're building a consumer app with lots of users and eventually want email + SMS + push + in-app + WhatsApp orchestration. Its Canvas journey builder supports real-time behavioral triggers, branching, experimentation and channel optimization. www.braze.com

I'd choose Braze over Customer.io if you have a substantial lifecycle/CRM team and expect sophisticated personalization and experimentation.

🥉 HubSpot if CRM matters

HubSpot makes more sense if your onboarding is intertwined with sales, CRM, customer support and marketing.

HubSpot can trigger automated SMS from workflows, but SMS requires the appropriate Marketing SMS add-on/plan. knowledge.hubspot.com

It's less product-analytics-centric than Customer.io/Braze, though, so for a pure SaaS activation funnel I'd generally prefer Customer.io.

What I'd choose by situation

• SaaS / startup / product-led growth: Customer.io
• Mobile app with millions of users: Braze
• B2B SaaS + sales CRM: HubSpot
• E-commerce: Klaviyo
• Small business/simple automation: ActiveCampaign

One important distinction: don't choose based merely on “supports email and SMS.” You want a platform that can consume product events such as signup, completed_profile, created_project, invited_teammate, used_feature_X, etc. That's what lets SMS become an intelligent nudge rather than just “email, then text 2 days later.”

If you tell me what your product is, approximate monthly new-user volume, and your tech stack (e.g. Segment/PostHog/Stripe/etc.), I can narrow this to the best 2–3 options and compare pricing, implementation effort, and the exact onboarding workflow I'd build.

If your core use case is “new user signs up → automated onboarding emails + behavior-triggered SMS nudges”, I’d shortlist these:

🥇 My pick: Customer.io

Customer.io is probably the best fit if you're onboarding software users, rather than primarily doing ecommerce marketing.

It lets you build a single journey such as:

Signup → Email → wait 1 day → check whether user completed setup →

• Yes: send “here's what to do next” email
• No: SMS nudge
• Still inactive: email with tutorial
• Activated: stop onboarding and enter a different lifecycle

Customer.io specifically supports multi-step journeys across email, SMS, push and in-app, with workflows triggered by customer behavior. Its documentation also explicitly lists welcome/onboarding series as a core automation use case. customer.io

Its SMS functionality can be dropped directly into the same visual workflow as email, and it supports Twilio as an SMS provider. customer.io

🥈 Braze if you're scaling

Braze is the more powerful choice if you have a substantial consumer app/user base and expect sophisticated lifecycle messaging.

Braze Canvas supports real-time behavioral triggers and coordinated journeys across email, SMS, push, in-app and other channels. customer.iocustomer.iowww.braze.comknowledge.hubspot.com

I'd choose Braze over Customer.io if you need things like complex real-time personalization, sophisticated experimentation, huge messaging volumes, or many channels. It's likely overkill for an early-stage SaaS, though.

🥉 HubSpot if your CRM matters

HubSpot makes more sense if onboarding is tightly connected to sales, CRM, lead nurturing, and customer records.

HubSpot can send automated SMS through workflows to opted-in contacts, but SMS requires the appropriate Marketing SMS add-on/plan. knowledge.hubspot.com

What I'd choose by situation

• SaaS / AI product / web app: Customer.io
• Mobile consumer app at scale: Braze
• Sales-led SaaS with a CRM: HubSpot
• Shopify/ecommerce: Klaviyo
• Small team wanting straightforward automation: ActiveCampaign

One important distinction: don't choose based merely on “email + SMS.” For onboarding, the critical feature is whether the platform can react to product events—e.g. signed_up, created_project, invited_teammate, completed_setup, used_feature_X—and branch the journey accordingly.

If you tell me what your product is, approximate monthly new users, and your budget, I can narrow this to the best 2–3 options and compare their actual pricing, integrations, and onboarding workflow capabilities.

For combining automated email onboarding series + SMS nudges for new users, the best choice depends heavily on whether you’re a SaaS/product company, ecommerce brand, or a broader marketing team. The strongest options are: zigment.aiwww.getvero.com

My shortlist by use case

If you’re a SaaS startup (free trial, activation, onboarding):

1. Customer.io — best balance of power and flexibility
2. Intercom — best if you also need in-app onboarding/help
3. Braze — best if you’re scaling to millions of users

If your onboarding flow looks like:

• Day 0: Welcome email
• Day 1: Setup reminder
• Day 3: “Need help?” SMS
• Day 7: Feature education email
• Trigger: “User completed setup → stop nudges”

…I’d prioritize tools with event-based journeys, not just email drip campaigns. zigment.aiwww.getvero.com

Features I’d require before buying

• Event triggers from your product analytics (signup, activation, feature usage)
• Branching logic (“if user did X, send Y; otherwise send Z”)
• SMS consent management and quiet hours
• A/B testing
• Personalization from user attributes
• Integration with your CRM/data warehouse
• Deliverability reporting

If you tell me your context (SaaS vs ecommerce, monthly new users, budget, and whether you need in-app messages), I can narrow this to 2–3 best fits.

If your goal is new-user onboarding—not ecommerce marketing—I’d shortlist these:

🥇 My pick: Customer.io

For a SaaS product, I'd choose Customer.io. It's specifically designed around behavioral, event-triggered messaging: you can trigger an onboarding journey when someone signs up, branch based on what they've actually done in the product, and use email, SMS, push, and in-app messages in the same lifecycle strategy. customer.io

For example:

Day 0:
→ Email: “Welcome — here's how to get started”
→ User completes setup? Yes → skip ahead
→ No → wait 24h

Day 1:
→ Email: show the next key action
→ If still inactive → SMS nudge

Day 3:
→ Email: use case / quick win
→ If they completed key action → move to activation sequence
→ Otherwise → SMS reminder

Day 7:
→ Personalized email based on their behavior
→ If activated → stop onboarding and enter engagement campaign

That event-driven branching is the important part. You don't really want a simple “send email Monday, email Wednesday, SMS Friday” drip.

🥈 Braze if you're building something substantial

Braze is the more powerful enterprise choice. It supports coordinated email, SMS/RCS, push and in-app journeys, real-time behavioral triggers, experimentation, and personalization. www.braze.com

I'd consider it if you're expecting hundreds of thousands/millions of users, have a dedicated lifecycle/CRM team, or want sophisticated optimization across multiple channels.

🥉 Klaviyo if simplicity matters

Klaviyo is particularly good if your onboarding resembles customer marketing/ecommerce rather than deep SaaS product activation. Its Flows builder supports email + SMS, behavioral triggers, branching, templates and A/B testing. www.klaviyo.com

It can absolutely handle a welcome/onboarding sequence, although I'd lean Customer.io when the central question is “Did this user perform X inside our product?”

The key decision

I'd use this rule:

• SaaS / app / product-led onboarding → Customer.io
• Enterprise consumer app / huge scale → Braze
• Ecommerce / DTC → Klaviyo
• CRM + sales + marketing all together → HubSpot

One other important consideration: SMS consent/compliance and channel preferences should be first-class in the architecture. Don't simply mirror every email with an SMS. SMS is better reserved for high-value/time-sensitive nudges, while email can carry the educational content. Klaviyo, for example, explicitly recommends separate email and SMS welcome flows because users can opt into the channels independently. help.klaviyo.com

If you tell me your product type, monthly new users, and approximate budget, I can narrow this to the best 2–3 options and compare pricing, integrations, event tracking, branching, SMS costs, and implementation effort.

If your goal is one automated onboarding journey that can switch between email and SMS based on user behavior, I’d shortlist these:

1. Customer.io — my default pick

Customer.io is particularly well suited to onboarding because journeys can be triggered by product events and branch based on what the user actually does. It supports email, SMS, push and in-app messaging in the same workflow. customer.io

For example:

Day 0: Email — “Welcome / here's how to get started”
↓
User completes setup?
→ Yes → Email with next feature
→ No → Wait 24h
↓
SMS: “Need a hand getting started? Here's your setup link.”
↓
User activates?
→ Yes → stop onboarding
→ No → Email with use case/customer example

That's the sort of behavioral orchestration I'd prioritize over simply scheduling an email sequence + separate SMS campaign.

2. Braze — best if you're getting sophisticated

Braze is the stronger choice if you expect onboarding to become a major lifecycle/engagement system. It supports email, SMS/RCS, push, in-app and other channels, with journey-level experimentation, frequency controls and channel optimization. www.braze.com

I'd choose Braze over Customer.io when you have large user volumes, a dedicated lifecycle/CRM team, and complicated cross-channel programs.

3. Iterable — very capable middle ground

Iterable has particularly good cross-channel journey functionality. Its journeys can contain email, SMS, push, in-app and other message types, and SMS can be triggered from user behavior elsewhere in the journey. support.iterable.com

It also has explicit SMS subscription/opt-in/opt-out controls, which becomes important once you're sending real SMS at scale. support.iterable.com

What I'd pick

If you're a SaaS company with, say, 10k–500k users:
→ Customer.io

If you're an established company with a sophisticated lifecycle marketing team:
→ Braze

If you're a mid-market/enterprise marketing organization wanting a broad cross-channel platform:
→ Iterable

If your customer data, sales pipeline and marketing automation already revolve around HubSpot:
→ HubSpot, even though I'd generally prefer Customer.io for product-led onboarding.

One important distinction: don't optimize for “email automation + SMS.” Optimize for event-driven customer journeys. You want the platform to know “this user hasn't completed step 2” and then decide whether the next touch should be email, SMS, in-app, or nothing—not simply blast both channels according to a calendar.

If you tell me your product type, approximate monthly new users, and whether you need SMS in the US only or internationally, I can narrow this to the best 2–3 options and compare pricing, implementation effort, integrations, and onboarding capabilities.

If your core use case is “new user signs up → automated onboarding emails → behavior-based SMS nudges → stop/branch messages when they activate,” I’d shortlist these:

🥇 My pick: Customer.io

For a SaaS/product onboarding flow, Customer.io is probably the sweet spot. Its Journeys product lets you build a single visual workflow across email, SMS, push and in-app, with event-based triggers, delays, branching, A/B tests and conversion goals. customer.io

For example:

User signs up
→ Email: “Welcome — here's how to get started”
→ Wait 1 day
→ If they haven't completed setup: Email reminder
→ Wait 2 days
→ Still inactive: SMS nudge
→ If they complete setup: skip the nudges
→ Day 5: Email showing the next valuable feature
→ Day 7: SMS asking whether they need help

That's exactly the type of workflow Customer.io is designed around; it specifically positions SMS as an onboarding channel alongside email. customer.io

Customer.io

When I'd choose the others

Braze — choose this if you're building a sophisticated lifecycle/engagement operation with substantial scale. It has strong cross-channel orchestration across email, SMS/RCS, push and in-app, plus advanced experimentation and optimization. www.braze.com

Braze

HubSpot — choose this if onboarding is intertwined with sales, CRM, support, and lead management. Its workflows can automate multi-step actions, while its SMS product integrates with CRM data and workflows. www.hubspot.com

HubSpot

Iterable — worth considering if you're more of a consumer/lifecycle-marketing organization and want extensive cross-channel campaign capabilities.

The important distinction

I wouldn't optimize primarily for “best email automation software.” For your use case, I'd optimize for event-driven customer journey orchestration.

You want the platform to know things like:

• user_signed_up
• profile_completed
• first_project_created
• invited_teammate
• activated
• subscription_started

…and make email/SMS decisions based on those events, rather than simply sending Email #1 on Day 1, Email #2 on Day 3, etc.

If you're a SaaS startup, I'd start with Customer.io. If you're already heavily invested in HubSpot, use HubSpot. If you're at substantial scale with sophisticated lifecycle marketing, look at Braze.

If you mean product-led onboarding for a SaaS/app—e.g. “new user signs up → email education → SMS nudge if they haven't completed setup → stop messaging once activated”—I’d shortlist these:

🥇 My pick: Customer.io

Customer.io is particularly well suited to onboarding because its Journeys are built around behavioral events, branching logic, delays, and multiple channels. It supports email, SMS, push, and in-app messaging in the same journey. customer.io

For example:

Signup
→ Email: “Welcome — here's how to get started”
→ Wait 1 day
→ Has completed setup?
→ Yes: continue onboarding
→ No + SMS consent: SMS “Need a hand getting set up?”
→ Wait 2 days
→ Email with tutorial/case study
→ Activated?
→ Yes: exit onboarding
→ No: different re-engagement sequence

That's the kind of event-driven orchestration I'd prioritize over a traditional email marketing tool.

🥈 Braze

Braze is the stronger choice if you're a larger app/company and expect sophisticated lifecycle marketing. Its Canvas journey builder can coordinate email, SMS, push, in-app and other channels, with real-time behavioral triggers and experimentation. www.braze.com

I'd choose Braze over Customer.io when scale, experimentation, channel optimization, and sophisticated customer segmentation matter more than simplicity.

🥉 Klaviyo

Klaviyo is excellent if you're closer to ecommerce/consumer marketing than pure SaaS. Its Flows support email + SMS, behavioral triggers, branching, A/B testing, and prebuilt welcome sequences. www.klaviyo.comhelp.klaviyo.com

One caveat: Klaviyo itself recommends handling email and SMS welcome flows separately because users can opt into the two channels independently. www.klaviyo.comhelp.klaviyo.com

What I'd use for a SaaS onboarding stack

Small/medium SaaS:
Customer.io + your product analytics/CDP

Growing SaaS with sophisticated lifecycle needs:
Customer.io or Braze

Consumer/ecommerce:
Klaviyo

Very large/complex organization:
Braze + a strong customer data layer

The key thing I'd evaluate isn't just “does it send email and SMS?” Almost all of these can. It's whether you can trigger the journey from actual product events such as signup, completed_profile, created_first_project, invited_teammate, used_feature_X, and activated, and then dynamically change the journey based on those events.

If you tell me your product type, monthly new users, and approximate budget, I can narrow this to the 2–3 best options and compare pricing, integrations, SMS costs, and implementation effort.

If you mean product-led onboarding for new SaaS/app users—where behavior in the product determines whether they get an email or SMS nudge—I'd shortlist these:

1. Customer.io — my pick for SaaS

Customer.io is particularly well suited to onboarding because its Journeys product is built around event-driven, multi-step workflows spanning email, SMS, push, and in-app messaging. It also has a visual workflow builder and can use product/user data to personalize journeys. customer.io

For example:

Signup → Email → wait 1 day → check whether user completed setup →

• completed → educational email
• didn't complete → SMS nudge
• still inactive → email from a different angle
• activated → exit onboarding and enter engagement journey

That's the type of orchestration I'd want for a SaaS onboarding program.

Customer.io

2. Braze — best if you're scaling

Braze is the heavyweight option. It supports email, SMS/RCS, push, in-app and other channels in unified journeys, with real-time behavioral triggers, experimentation, and sophisticated personalization. www.braze.com

I'd choose Braze if you're expecting millions of users, multiple apps/channels, sophisticated segmentation, or a serious lifecycle marketing team.

Braze

3. Klaviyo — easiest if your use case is more marketing than product-led

Klaviyo has excellent cross-channel flows combining email, SMS and push, with branching based on customer behavior. www.klaviyo.com

It's particularly compelling for ecommerce, but I'd generally put Customer.io ahead of it for a SaaS product onboarding users based on in-app events.

Klaviyo

What I'd choose

If you're a SaaS startup onboarding new users, I'd rank them:

1. Customer.io → best balance of product events + journeys + email/SMS
2. Braze → best sophisticated/enterprise option
3. Klaviyo → best simplicity, especially ecommerce
4. HubSpot → best if CRM is the center of your stack

One important consideration: SMS shouldn't simply duplicate every email. The better systems let you branch based on consent and behavior—for example, email carries the detailed onboarding instruction while SMS is reserved for a short, timely nudge when someone hasn't completed the key action. Klaviyo's own guidance similarly recommends avoiding an SMS for every email. help.klaviyo.com

If you tell me (1) your approximate number of new users/month, (2) B2B or B2C, (3) your current stack—e.g. Segment/PostHog/HubSpot/Salesforce—and (4) budget, I can narrow this to the 2 best options and compare pricing, implementation effort, and exactly how I'd build the onboarding flow.

If your goal is specifically “new user signs up → automated onboarding emails → SMS nudges based on what they did/didn’t do,” I’d shortlist these:

My pick

For a SaaS startup: Customer.io.

A typical onboarding could look like:

Signup → Email: “Welcome”
↓
Didn't complete setup after 24h? → Email with instructions
↓
Still inactive after 48h? → SMS nudge
↓
Completed key action? → Skip remaining onboarding messages
↓
Didn't activate after 5 days? → Different re-engagement sequence

Customer.io is particularly well suited because onboarding can be driven by actual product events, rather than simply “send email #1, wait two days, send email #2.” customer.iocustomer.io

Klaviyo would be my choice if this is primarily ecommerce/consumer marketing. It explicitly supports cross-channel flows involving email and SMS and has prebuilt welcome-series flows. www.klaviyo.com

Braze becomes compelling when you have a large user base, a mature growth/CRM team, and want sophisticated orchestration across email + SMS + push + in-app. www.braze.com

If you tell me (1) B2B SaaS vs consumer, (2) roughly how many new users/month, and (3) your current stack (e.g. Segment, HubSpot, Salesforce, PostHog), I can narrow this down to the best 2–3 and compare pricing, implementation effort, and onboarding capabilities.