ChatGPT answers, unedited

For an agency that needs to run, clone, test, and compare automated lifecycle campaigns across multiple clients, the best tool depends on whether you mean email/SMS lifecycle marketing, full CRM journeys, or agency operations. The shortlist looks like this: AiMarketer Tekpon

My practical picks by agency model

• 10–100 SMB clients (especially local businesses): GoHighLevel is usually the most agency-native because of sub-accounts and white-label capabilities. Tekpon
• B2B lifecycle agency managing complex nurture programs: HubSpot or ActiveCampaign. US Tech Automations
• Ecommerce retention agency: Klaviyo.
• SaaS/product lifecycle consulting: Customer.io.
• Agency running many experiments and comparing performance: pair a campaign platform with a reporting/analytics layer rather than expecting one tool to do everything. SlickText

For your specific phrase — “run and compare automated lifecycle campaigns for several clients at once” — I’d prioritize these features:

1. Client/account separation (no risk of data mixing)
2. Reusable campaign templates (clone journeys across clients)
3. A/B testing and holdouts
4. Cross-client reporting dashboards
5. Approval workflows before sends
6. Event-level analytics (not just opens/clicks)

If you tell me:

• number of clients (5, 20, 100+),
• channels (email only vs email/SMS/push),
• client type (SaaS, ecommerce, local SMB, B2B),
• and whether clients need login access,

I can narrow it to a top 2–3 stack.

If by “automated lifecycle campaigns” you mean things like onboarding, activation, trial conversion, churn prevention, re-engagement, and retention—and your agency needs to operate several client accounts and compare campaign performance across them—I’d shortlist these:

My take

For a lifecycle-focused agency, I'd start with Customer.io.

Its workspace model is particularly relevant: a single Customer.io account can contain multiple workspaces, with separate people, data, messages, and integrations; team members can also be given workspace-specific access. docs.customer.io

That maps nicely to:

Agency → Client A workspace / Client B workspace / Client C workspace → standardized lifecycle templates → client-specific variants → shared reporting framework

Braze becomes more compelling when you're managing sophisticated, high-volume lifecycle programs. Its Canvas system supports multi-step, cross-channel journeys, experimentation, and optimization, and Braze documents A/B testing and multi-armed-bandit optimization across campaign dimensions. www.sec.gov

GoHighLevel is the more agency-native choice if the clients are primarily SMBs and you want isolated client sub-accounts plus white-labeling/reselling. Current 2026 comparisons specifically highlight its sub-account architecture and white-label/SaaS capabilities. aimarketer.com

One important distinction

If your real requirement is:

“Build one lifecycle campaign → deploy variations to 20 clients → automatically collect results → compare them in one agency dashboard”

then I would not choose solely based on which platform has the best campaign builder. The critical feature is the agency-level experimentation/reporting layer.

I'd evaluate:

1. Template cloning across clients
2. Client/data isolation
3. Ability to standardize campaign definitions
4. A/B testing at campaign/journey level
5. Normalized KPIs across clients
6. Portfolio-level reporting
7. Client-specific integrations/data schemas
8. Approval workflows
9. API/export access
10. Cost as client count grows

If you tell me what kind of clients you have (SaaS, ecommerce, local businesses, etc.), roughly how many, and whether the campaigns are email/SMS/push/in-app, I can narrow this to 2–3 platforms and show exactly how I'd structure the agency workflow.

For an agency that needs to run, clone, test, and compare automated lifecycle campaigns across multiple clients, the best tool depends on whether you mean email/SMS lifecycle marketing, full CRM automation, or agency operations. The strongest options are:

ConvertMate Agency Software Lab## My shortlist by agency model

If you manage 10–100 smaller clients

HighLevel is usually the closest match. Its structure is built around agencies managing multiple client accounts, with separate client environments and reusable campaign setups. AiMarketer Agency Software Lab

Good for:

• Lead nurture sequences
• Appointment funnels
• SMS/email follow-ups
• Client reporting
• Replicating proven campaigns across accounts

If you run sophisticated lifecycle marketing

Choose Customer.io, ActiveCampaign, or HubSpot.

Good for:

• Trial → activation → retention journeys
• Behavioral triggers
• Cohort comparisons
• A/B testing
• Complex segmentation

Customer.io is particularly strong when campaigns depend on product events (e.g., “user completed step 2 but not step 3”). ConvertMate

If you are an ecommerce lifecycle agency

Look at Klaviyo first.

Good for:

• Welcome flows
• Abandoned cart
• Post-purchase sequences
• VIP/customer value segmentation
• Revenue reporting

Features I would prioritize for an agency

Whatever platform you choose, look for:

• Client workspaces/sub-accounts — prevents data mixing
• Campaign templates or cloning — deploy proven journeys quickly
• Cross-client reporting — compare performance without exporting spreadsheets
• Experiment tracking — compare variants, audiences, and timing
• Approval workflows — clients can review before launches
• Role permissions — protect client data
• API/webhooks — connect CRMs, warehouses, analytics tools

A common agency stack is:

• HighLevel or HubSpot for client management + CRM
• Customer.io/ActiveCampaign/Klaviyo for advanced lifecycle execution
• Looker Studio or a BI tool for cross-client reporting

If you tell me:

1. how many clients you manage,
2. whether they are mostly SaaS, ecommerce, local businesses, or B2B, and
3. whether clients need login access,

I can narrow this to 2–3 platforms.

If you mean an agency managing lifecycle/CRM automation for multiple clients and wanting to launch standardized experiments and compare results across accounts, my top pick is Customer.io.

My shortlist

Why I'd choose Customer.io: its workspace model maps unusually well to an agency structure. You can create separate workspaces for different products/sites, with each workspace having its own profiles, automations, metrics and data; workspaces can also be used as isolated testing environments. You can copy workflow actions between workspaces, which is particularly useful when you're repeatedly deploying a proven lifecycle framework to different clients. Customer.io Customer.io

It also supports email, push, in-app, SMS and other channels, so you're not limited to email automation. Customer.io Customer.io

But there's an important distinction

If your actual goal is:

"I want to build the same lifecycle campaign for 10–50 clients, change the inputs, run controlled variants, and get one agency-wide dashboard showing which strategy wins."

Then Customer.io isn't quite the complete answer by itself. Its workspaces give you client isolation and reusable workflows, but you'll probably want a separate agency-level analytics/experimentation layer to normalize results across clients.

If you're doing large enterprise/mobile clients, I'd instead seriously consider Braze. Its Canvas supports multiple journey variants and automatic optimization based on variant performance, and Braze is built around cross-channel lifecycle orchestration. SEC Braze

What I'd pick by agency type

• 5–30 SaaS/product clients: Customer.io
• Large consumer/mobile clients: Braze
• Large mid-market/enterprise marketing programs: Iterable
• Ecommerce/DTC portfolio: Klaviyo
• B2B clients where CRM + marketing are inseparable: HubSpot

One caveat: none of these is really purpose-built as an "agency operating system for lifecycle experimentation." If that's specifically the product you're looking for—client isolation + reusable campaign templates + simultaneous execution + cross-client experiment comparison + agency-wide reporting—that's a narrower category, and I can compare the best tools specifically against those requirements. trypropel.ai

Why I'd choose Customer.io: its workspace model maps unusually well to an agency structure. You can create separate workspaces for different products/sites, with each workspace having its own profiles, automations, metrics and data; workspaces can also be used as isolated testing environments. You can copy workflow actions between workspaces, which is particularly useful when you're repeatedly deploying a proven lifecycle framework to different clients. Customer.io Customer.io

It also supports email, push, in-app, SMS and other channels, so you're not limited to email automation. Customer.io Customer.io

But there's an important distinction

If your actual goal is:

"I want to build the same lifecycle campaign for 10–50 clients, change the inputs, run controlled variants, and get one agency-wide dashboard showing which strategy wins."

Then Customer.io isn't quite the complete answer by itself. Its workspaces give you client isolation and reusable workflows, but you'll probably want a separate agency-level analytics/experimentation layer to normalize results across clients.

If you're doing large enterprise/mobile clients, I'd instead seriously consider Braze. Its Canvas supports multiple journey variants and automatic optimization based on variant performance, and Braze is built around cross-channel lifecycle orchestration.

If your main requirement is an agency running lifecycle automation for multiple clients and systematically comparing experiments, I’d shortlist these:

My pick: Customer.io

Customer.io is probably the best fit if campaign testing and lifecycle performance are the heart of your service.

It supports multi-step, event-triggered journeys across email, SMS, push and in-app, with branching, conversion goals and A/B testing. You can also copy workflow components between workspaces, which is useful when you're taking a proven client journey and adapting it for another client. Customer.io Customer.io Customer.io

The important caveat: Customer.io workspaces are intentionally isolated—profiles, automations and metrics aren't shared between them. So it's excellent for replicating and comparing methodology across clients, but less ideal if you want a single agency dashboard that automatically aggregates every client's experiments. Customer.io

If cross-client experimentation is the priority: Braze

Braze is stronger for sophisticated experimentation. Its Canvas supports experiments across journeys, paths and individual messages, plus control groups and optimization against conversion/retention/revenue KPIs. Braze also now supports cross-workspace operations through its MCP Server. Braze Braze Braze

I'd choose it if your agency is working with larger clients, substantial user volumes, and serious lifecycle/retention programs. It's probably overkill for a typical SMB agency.

If you want agency operations + CRM: HubSpot

HubSpot is the better choice when the agency needs to manage CRM, lead nurture, marketing automation and reporting in addition to lifecycle campaigns. Its current Campaigns tooling can compare up to 10 campaigns and provides multi-campaign reporting. HubSpot HubSpot Knowledge Base

Bottom line:

• Customer.io → best balance of lifecycle automation + experimentation.
• Braze → best for advanced experimentation at enterprise scale.
• HubSpot → best if the agency also needs CRM/sales operations.
• ActiveCampaign → worth considering for a more SMB-oriented agency stack.

If by “compare campaigns” you mean “run the same lifecycle experiment across 10–50 clients and get a single dashboard showing which variant wins across the entire client portfolio,” that's a more specific requirement—and I'd use a different shortlist.

Customer.io is probably the best fit if campaign testing and lifecycle performance are the heart of your service.

It supports multi-step, event-triggered journeys across email, SMS, push and in-app, with branching, conversion goals and A/B testing. You can also copy workflow components between workspaces, which is useful when you're taking a proven client journey and adapting it for another client. Customer.io Customer.io Customer.io

The important caveat: Customer.io workspaces are intentionally isolated—profiles, automations and metrics aren't shared between them. So it's excellent for replicating and comparing methodology across clients, but less ideal if you want a single agency dashboard that automatically aggregates every client's experiments. Customer.io

If cross-client experimentation is the priority: Braze

Braze is stronger for sophisticated experimentation. Its Canvas supports experiments across journeys, paths and individual messages, plus control groups and optimization against conversion/retention/revenue KPIs. Braze also now supports cross-workspace operations through its MCP Server. www-origin.braze.com braze.com braze.com

I'd choose it if your agency is working with larger clients, substantial user volumes, and serious lifecycle/retention programs. It's probably overkill for a typical SMB agency.

If you want agency operations + CRM: HubSpot

If your agency needs to run lifecycle campaigns for multiple clients and compare what works across accounts, I’d shortlist these:

My pick: ActiveCampaign

For a typical lifecycle/CRM agency, ActiveCampaign is probably the best balance of automation depth and agency usability. Its workflow builder is particularly strong for branching journeys, behavioral triggers, nurture, re-engagement, lead scoring, etc. US Tech Automations Hack'celeration

The catch: it isn't really designed as a single cross-client experimentation/analytics layer. Client accounts remain relatively separate, so comparing "Campaign A vs. Campaign B across 15 clients" takes some reporting work.

If cross-client comparison is the core requirement

I'd actually look at an architecture rather than just one marketing platform:

Client automation platform → standardized campaign templates → centralized analytics/BI layer

For example:

• HubSpot if clients are mostly B2B and you need CRM + attribution.
• Klaviyo if they're mostly ecommerce brands.
• Customer.io if you're working with SaaS/product-led companies and event-driven lifecycle journeys.
• A central warehouse/dashboard then lets your agency compare standardized metrics across clients: activation rate, conversion, revenue/contact, unsubscribe rate, experiment lift, etc.

Customer.io is particularly compelling when lifecycle campaigns are driven by product events rather than simple email-list conditions. CodeDrips Customer.io

One interesting agency-native option

transpond.io is worth a look if you specifically want one agency workspace covering multiple clients, reusable automation templates, client-specific campaigns, reporting, and white-labeling. It explicitly positions itself around that workflow. Transpond

If you tell me what your clients are mostly like — SaaS, ecommerce, B2B, local businesses, etc. — and roughly how many clients (5, 20, 100+), I can narrow this to the best 2–3 options and compare pricing + multi-client experimentation capabilities.

If you mean an agency managing lifecycle/CRM campaigns for multiple client brands, my top pick is Customer.io—with Braze as the stronger choice for larger, more sophisticated enterprise clients.

My shortlist

Why I'd pick Customer.io

For an agency, the important combination is isolated client environments + reusable campaign architecture + easy experimentation + reporting.

Customer.io lets you create separate workspaces, with each workspace having its own profiles, automations, metrics and data. You can also copy workflow actions between workspaces, which is particularly useful when you're deploying a proven lifecycle framework across clients. Customer.io Customer.io

Its journey builder supports:

• Multi-step behavioral journeys
• Email, SMS, push, in-app and other channels
• Branching and conditional logic
• A/B testing
• Conversion goals
• Real-time behavioral triggers
• Workflow-level analytics Customer.io Customer.io

That makes a setup like this fairly natural:

Agency → Client A workspace → Client B workspace → Client C workspace

Then you can maintain standardized templates such as:

• Welcome/onboarding
• Activation
• Abandoned signup
• Trial conversion
• Upgrade
• Churn prevention
• Win-back
• Post-purchase
• Cross-sell

…and adapt the same underlying playbook for each client.

Where Braze wins

If your agency works with large companies with sophisticated data teams, I'd seriously consider Braze.

Braze Canvas is particularly strong for comparing entire lifecycle strategies, not merely subject-line A/B tests. It supports multiple journey variants, control groups, channel/cadence experimentation and automated optimization. SEC Braze

For example, you could test:

Variant A: Email → 2-day delay → Push
Variant B: Push → In-app → Email
Variant C: Email → SMS → Push
Control: Nothing

and compare downstream conversion/revenue rather than just opens and clicks. Braze documents exactly this kind of multi-variant lifecycle experimentation. Braze

My recommendation

For a typical lifecycle marketing agency: Customer.io.

For an enterprise lifecycle/CRM agency: Braze.

The deciding question is really how many clients, how complex their data is, and whether you're trying to run a standardized agency operating system across accounts.

If you tell me roughly 5 clients vs. 50+ clients, B2B vs. ecommerce vs. SaaS, and whether you need email-only or email + SMS + push, I can narrow this to the best 2–3 tools and compare pricing, multi-client management, templates/reuse, reporting, and white-label/agency workflows.

If you mean an agency that operates lifecycle/CRM programs for multiple clients and wants to launch experiments, compare results, and reuse campaign patterns across accounts, I’d shortlist these:

My pick: Customer.io

For an agency, Customer.io is particularly interesting because you can maintain multiple workspaces under one account, with each workspace keeping its own profiles, data, messages, integrations, and settings. Customer.io Customer.io

It also supports automated journeys, A/B testing, conversion goals, and cross-channel messaging. Customer.io Customer.io And Customer.io explicitly has a partner program aimed at lifecycle marketing/development agencies doing implementation and campaign execution. Customer.io

That makes the agency operating model fairly clean:

• Client A → Workspace A
• Client B → Workspace B
• Client C → Workspace C
• Your agency team gets appropriate access across workspaces.
• Build standardized lifecycle templates/playbooks.
• Run A/B tests within each client.
• Compare outcomes using a common reporting framework outside/alongside the platform.

Where I'd choose Braze instead

If your clients are large consumer apps with substantial mobile usage and sophisticated email + push + in-app + SMS/WhatsApp journeys, I'd lean toward braze.com. Braze is built around sophisticated journey orchestration and now has AI-powered decisioning/optimization capabilities. Braze

The tradeoff is that it's considerably more enterprise-oriented, so it can be overkill if you're managing dozens of smaller clients.

One important distinction

If by “run and compare automated lifecycle campaigns for several clients at once” you mean something more specific—e.g. one agency dashboard where you can clone the same lifecycle experiment across 10 clients and compare performance across clients—that's a different requirement. Most lifecycle platforms are designed to isolate each client's data rather than give an agency a true multi-client experimentation layer.

If that's what you're after, I would not automatically pick Customer.io/Braze. I'd look for an agency-specific orchestration/reporting layer on top of them.

If your agency manages multiple clients and wants to build, run, test, and compare lifecycle campaigns across accounts, my first choice would be Klaviyo for ecommerce/DTC clients.

Best options

🥇 Klaviyo — strongest agency choice for ecommerce

Klaviyo has a particularly useful combination for your use case: Portfolio lets you manage multiple client/brand accounts from a centralized view, clone assets across accounts, and create portfolio-level reporting. You can compare individual accounts and drill into campaign/flow performance without logging into each account separately. Klaviyo Academy Klaviyo Help Center

It also has built-in benchmarks that compare campaigns and flows against similar companies, so an agency can answer things like:

"Client A's abandoned-cart flow is converting at 4.2%, while Client B's is at 2.1%. Which implementation is better?"

And separately:

"How do both clients compare with the relevant industry/peer benchmark?"

Klaviyo's benchmarks cover campaign and flow performance, with peer groups based on characteristics such as industry and company size. Klaviyo Academy Klaviyo Help Center

That's unusually well aligned with an agency operating model.

🥈 Customer.io — better if clients are SaaS

I'd pick Customer.io over Klaviyo if your clients are primarily SaaS/product companies where lifecycle triggers depend on product events rather than ecommerce transactions.

It supports sophisticated event-driven journeys, experimentation, and multiple workspaces. Its current platform also explicitly supports campaign experiments and conversion-goal measurement. Customer.io Customer.io

The downside for an agency is that workspaces are isolated—profiles, automations, metrics, etc. aren't shared between them—so it isn't as naturally designed for the "one agency dashboard across 20 clients" use case as Klaviyo Portfolio. Customer.io

My recommendation

If you're building an agency operating system, I'd rank them:

Ecommerce agency:
Klaviyo → HubSpot → Customer.io → Braze

SaaS lifecycle agency:
Customer.io → HubSpot → Braze → Klaviyo

If your key requirement is specifically "run experiments across clients and learn which lifecycle playbooks consistently win": I'd actually look at Klaviyo + a separate agency-level analytics layer. Klaviyo gives you the multi-account management and benchmarking; a warehouse/BI layer can normalize metrics across clients so you can compare things like welcome flow → activation, 30-day retention, revenue per recipient, etc., on a genuinely apples-to-apples basis.

If you tell me what kind of clients you manage (ecommerce, SaaS, subscriptions, B2B) and roughly how many client accounts, I can narrow this down to the best 2–3 tools and explain exactly how I'd structure the agency stack.

If you mean an agency operating lifecycle automation for many clients simultaneously—with reusable campaigns, controlled experiments, and cross-client performance comparison—my top pick is Klaviyo Portfolio if most of your clients are ecommerce/DTC. It is unusually well suited to the agency workflow. Klaviyo Klaviyo Academy

My shortlist

Why Klaviyo stands out: Portfolio gives you a centralized view across client/brand accounts, lets you compare performance, clone campaigns and flows across accounts, share templates/segments, and manage users/permissions centrally. Klaviyo Klaviyo Academy

For example, an agency could build a standardized abandoned-cart / onboarding / win-back framework, clone it across 20 clients, customize each client's content and segments, then compare conversion performance across accounts. Klaviyo specifically supports cloning campaigns to multiple accounts and portfolio-level reporting. Klaviyo Academy

But there's an important distinction

If by "compare automated lifecycle campaigns" you mean:

"I want to run different versions of a lifecycle program across clients and determine which journey/strategy performs best."

I'd look beyond just the ESP. You want an agency operating layer with:

• Client/account isolation
• Reusable campaign templates
• Bulk deployment
• Experiment/version management
• Cross-client benchmarking
• Standardized KPIs
• Automated reporting
• Approval workflows
• Ideally, AI-assisted campaign generation

If your clients are not primarily Shopify/ecommerce, I'd probably choose Braze or Iterable instead. Braze is particularly strong when lifecycle involves sophisticated cross-channel orchestration, while Iterable tends to be a more accessible middle ground. alium.io suprsend.com

If you tell me your agency's client type (ecommerce, SaaS, apps, B2B, etc.) and roughly how many clients/accounts you're managing, I can narrow this to the best 2–3 tools and compare their agency/multi-account capabilities and pricing.

But there's an important distinction

If by "compare automated lifecycle campaigns" you mean:

"I want to run different versions of a lifecycle program across clients and determine which journey/strategy performs best."

I'd look beyond just the ESP. You want an agency operating layer with:

• Client/account isolation
• Reusable campaign templates
• Bulk deployment
• Experiment/version management
• Cross-client benchmarking
• Standardized KPIs
• Automated reporting
• Approval workflows
• Ideally, AI-assisted campaign generation

If your clients are not primarily Shopify/ecommerce, I'd probably choose Braze or Iterable instead. Braze is particularly strong when lifecycle involves sophisticated cross-channel orchestration, while Iterable tends to be a more accessible middle ground.

If you mean an agency that runs lifecycle programs for multiple clients and wants to launch A/B tests, compare performance, and reuse campaign playbooks across accounts, I’d shortlist these:

My pick: Customer.io

For a lifecycle-focused agency, I’d lean toward Customer.io if your clients are SaaS, apps, marketplaces, or other product-led businesses. It is particularly strong for event-triggered journeys, granular segmentation, and coordinating email/SMS/push/in-app messaging. Current comparisons also put it in the more accessible tier versus enterprise platforms like Braze and Iterable. Vero Oden

The bigger issue, though, is your phrase “run and compare … for several clients at once.” Most lifecycle platforms are designed around each client's individual workspace, rather than giving an agency a great cross-client experimentation/benchmarking layer. That distinction matters.

If cross-client operations are the priority

I'd look at GoHighLevel or ActiveCampaign. GoHighLevel is explicitly structured around agency sub-accounts and centralized management, while ActiveCampaign is a stronger choice when sophisticated email automation matters more than white-label/agency infrastructure. AiMarketer BestSends

If you're building a serious lifecycle experimentation practice

I'd actually consider a two-layer stack:

Customer.io/Braze/Klaviyo per client → centralized agency analytics layer

That lets you standardize things like:

• Welcome-flow conversion
• Activation rate
• Trial → paid
• Retention/reactivation
• Revenue per recipient
• Experiment lift
• Control vs. treatment performance
• Campaign performance across clients
• Which lifecycle playbooks consistently work across accounts

This is particularly compelling if the agency's differentiator is “we continuously test lifecycle programs across our client portfolio”, rather than simply “we manage your email.”

If you tell me what kinds of clients you serve (SaaS, ecommerce, B2B, apps, etc.) and roughly how many accounts, I can give you a much more specific top 3 + recommended stack, including which tool is best for cross-client campaign comparison.

If cross-client operations are the priority

I'd look at GoHighLevel or ActiveCampaign. GoHighLevel is explicitly structured around agency sub-accounts and centralized management, while ActiveCampaign is a stronger choice when sophisticated email automation matters more than white-label/agency infrastructure.

If you're building a serious lifecycle experimentation practice

I'd actually consider a two-layer stack:

Customer.io/Braze/Klaviyo per client → centralized agency analytics layer

That lets you standardize things like:

If your agency needs to run lifecycle campaigns for multiple clients and systematically compare what works, I’d shortlist these:

My pick: Customer.io

For an agency, I'd lean Customer.io if the clients are SaaS, subscription, marketplace, or other event-driven businesses. It gives you behavioral triggers, segmentation, journeys, experimentation, and relatively accessible pricing compared with Braze/Iterable. Vero DripAgent

The important distinction is that you want more than an email tool: you want to be able to take a repeatable lifecycle playbook—say activation → nurture → conversion → retention → win-back—deploy variations across clients, and compare outcomes by client/campaign/cohort.

If you're running a serious lifecycle agency

Iterable may actually be the strongest choice if clients have larger databases and budgets. Its current platform explicitly supports cross-channel journeys, experimentation, campaign analytics, reusable data, and centralized performance/attribution views. Iterable Iterable Support

Braze is the other enterprise contender. Its experimentation can test individual messages, journey paths, or entire journeys, and it supports automated optimization of the winning path. Braze

One caveat

If by "several clients at once" you mean one agency workspace where you can create client accounts, clone standardized campaigns, enforce approvals, and give each client its own dashboard, that's a somewhat different requirement. GoHighLevel and agency-oriented automation/reporting platforms become more interesting there. HighLevel Playbooks Orchestror

So my ranking for your exact use case:

1. Customer.io — best balance of lifecycle depth + experimentation + accessibility.
2. Iterable — best if you're managing sophisticated mid-market/enterprise clients.
3. Braze — best if clients need massive-scale omnichannel orchestration.
4. GoHighLevel — best if agency/client management and white-labeling are more important than sophisticated lifecycle experimentation.
5. ActiveCampaign — good if most clients are smaller and primarily email/SMS.

If you tell me what kind of clients you manage (SaaS, ecommerce, B2B, apps, etc.) and roughly how many clients, I can narrow this to the best 2–3 platforms and compare them specifically on cloning campaigns, A/B testing, client isolation, reporting, and price.

For an agency, I'd lean Customer.io if the clients are SaaS, subscription, marketplace, or other event-driven businesses. It gives you behavioral triggers, segmentation, journeys, experimentation, and relatively accessible pricing compared with Braze/Iterable. Vero DripAgent

The important distinction is that you want more than an email tool: you want to be able to take a repeatable lifecycle playbook—say activation → nurture → conversion → retention → win-back—deploy variations across clients, and compare outcomes by client/campaign/cohort.

If you're running a serious lifecycle agency

Iterable may actually be the strongest choice if clients have larger databases and budgets. Its current platform explicitly supports cross-channel journeys, experimentation, campaign analytics, reusable data, and centralized performance/attribution views. iterable.com support.iterable.com

Braze is the other enterprise contender. Its experimentation can test individual messages, journey paths, or entire journeys, and it supports automated optimization of the winning path. braze.com

One caveat

If by "several clients at once" you mean one agency workspace where you can create client accounts, clone standardized campaigns, enforce approvals, and give each client its own dashboard, that's a somewhat different requirement. GoHighLevel and agency-oriented automation/reporting platforms become more interesting there.

So my ranking for your exact use case:

If you mean an agency managing lifecycle/CRM automation for multiple clients and wanting to reuse, A/B test, and compare journeys across accounts, I’d shortlist these:

My pick: Customer.io

For the specific use case you described, Customer.io is probably the most interesting.

It lets you build behavioral, multi-step journeys across email, SMS, push, in-app, etc., with branching, A/B tests, conversion goals and cohort analysis. Customer.io Customer.io

More importantly for an agency, Customer.io's workspaces are isolated, with separate profiles, automations and metrics, while workflow actions can be copied between workspaces. That makes a "build once → adapt for Client B/C/D → compare results" operating model fairly natural. Customer.io

Its current Agent functionality also explicitly supports comparing automation metrics and surfacing underperforming messages, which is useful if you're trying to make campaign optimization systematic rather than manually reviewing every client's dashboard. Customer.io

customer.io

But if these are ecommerce clients: Klaviyo

I'd actually choose Klaviyo if most of your clients are Shopify/DTC brands.

Klaviyo's Portfolio is specifically designed for managing multiple brand accounts: you can monitor performance across accounts, filter reports, clone campaigns/flows, and share templates, forms and segments. Klaviyo Its agency-oriented tooling also supports comparing performance across multiple client accounts. Klaviyo Help Center

klaviyo.com

Where Braze fits

Braze is the heavier-duty choice. It's particularly compelling if you're running sophisticated app/web lifecycle programs and want serious experimentation—Canvas-level A/B/multivariate testing, control groups, and automated optimization are all part of the platform. Braze Braze now also supports cross-workspace operations and insights. Braze

braze.com

So my recommendation would be:

• Mostly Shopify/ecommerce clients → Klaviyo
• SaaS, apps, subscriptions, complex behavioral journeys → Customer.io
• Enterprise clients with big data/CRM teams → Braze
• Need a genuinely agency-friendly system for cloning + testing + benchmarking lifecycle programs → I'd start by evaluating Customer.io and Klaviyo head-to-head.

If you tell me what kind of clients you have (ecommerce, SaaS, apps, etc.) and roughly how many, I can narrow this down to the best 2–3 tools and compare their agency/multi-account workflows, pricing, experimentation, and reporting.

For the specific use case you described, Customer.io is probably the most interesting.

It lets you build behavioral, multi-step journeys across email, SMS, push, in-app, etc., with branching, A/B tests, conversion goals and cohort analysis. Customer.io Customer.io

More importantly for an agency, Customer.io's workspaces are isolated, with separate profiles, automations and metrics, while workflow actions can be copied between workspaces. That makes a "build once → adapt for Client B/C/D → compare results" operating model fairly natural. Customer.io

Its current Agent functionality also explicitly supports comparing automation metrics and surfacing underperforming messages, which is useful if you're trying to make campaign optimization systematic rather than manually reviewing every client's dashboard. Customer.io

customer.io

But if these are ecommerce clients: Klaviyo

I'd actually choose Klaviyo if most of your clients are Shopify/DTC brands.

Klaviyo's Portfolio is specifically designed for managing multiple brand accounts: you can monitor performance across accounts, filter reports, clone campaigns/flows, and share templates, forms and segments. klaviyo.com Its agency-oriented tooling also supports comparing performance across multiple client accounts. help.klaviyo.com

klaviyo.com

Where Braze fits

Braze is the heavier-duty choice. It's particularly compelling if you're running sophisticated app/web lifecycle programs and want serious experimentation—Canvas-level A/B/multivariate testing, control groups, and automated optimization are all part of the platform. Braze now also supports cross-workspace operations and insights.

For an agency that needs to run, test, and compare automated lifecycle campaigns across multiple clients, I’d prioritize platforms with:

• multi-client/workspace management
• reusable campaign templates
• A/B testing and experimentation
• cross-client reporting
• behavior-based journeys (not just email blasts)
• easy handoff/client visibility

The best options depend on your agency model:

My shortlist by agency type

If you run SaaS/app lifecycle campaigns

Pick: Customer.io or Iterable

You’ll want:

• onboarding journeys
• activation experiments
• churn prevention
• behavioral segmentation
• holdout tests

Customer.io is usually the more approachable option; Iterable is stronger for larger enterprise programs.

If you run ecommerce retention for many brands

Pick: Klaviyo

Best for:

• welcome flows
• abandoned cart
• post-purchase
• win-back
• VIP segmentation
• revenue reporting

If you are a general marketing agency managing many SMB clients

Pick: HighLevel or HubSpot

HighLevel is stronger if you want:

• one agency dashboard
• client sub-accounts
• white-label/reselling

HubSpot is stronger if clients need:

• CRM
• sales pipeline
• inbound marketing
• enterprise reporting

If you want to productize lifecycle marketing as a service

I’d lean toward:

1. Customer.io — for sophisticated lifecycle execution
2. Klaviyo — for ecommerce packages
3. HighLevel — for agency scalability/reselling
4. HubSpot — for higher-ticket B2B clients

What I would avoid

I’d be cautious with basic email tools (simple newsletter platforms) if your core service is lifecycle optimization. They often lack:

• journey experimentation
• event-triggered campaigns
• control groups
• cohort analysis
• reusable automation frameworks across clients

A strong agency stack is often:

• lifecycle platform (Customer.io/Klaviyo/Iterable)
• data layer (Segment, CDP, warehouse, or client analytics)
• reporting layer (Looker Studio, Tableau, HubSpot reporting, etc.)
• project templates for deploying the same playbooks across clients

If you tell me what kind of clients you serve (SaaS, ecommerce, B2B, local businesses), number of clients, and channels (email/SMS/push/in-app), I can narrow this to the top 2–3 choices.

If you mean an agency operating lifecycle campaigns for multiple clients and wanting to systematically test/compare what works across accounts, my top pick is Customer.io.

My shortlist

Why Customer.io: its Journeys can react to real-time events, branch on behavior, and run A/B and cohort tests with conversion goals—which is much closer to an experimentation/lifecycle operating system than a conventional email tool. Customer.io Customer.io

The important caveat is multi-client management. Customer.io is excellent for running sophisticated campaigns within each client, but it isn't fundamentally an agency-management layer. If your key requirement is one agency workspace where you can switch between 20+ client accounts, clone campaign templates, standardize experiments, and compare results across clients, I'd look harder at the agency-oriented architecture rather than simply picking the strongest lifecycle ESP.

For e-commerce clients, I'd choose Klaviyo instead; for B2B clients where CRM and sales workflows matter, HubSpot is generally the better fit. Current 2026 comparisons similarly position Klaviyo around e-commerce, Customer.io around event-driven/product-led lifecycle, and HubSpot around integrated CRM/marketing. Taqtics CodeDrips

If you're building an agency specifically around this workflow, I can also give you a 5-tool comparison focused specifically on multi-client workspaces + reusable campaigns + A/B testing + cross-client reporting, which is a slightly different question than “best lifecycle platform.”

If you mean an agency managing lifecycle automation for multiple client accounts, I’d shortlist these:

My pick: Iterable

Iterable is probably the best fit for a multi-client lifecycle agency if you have enough volume/budget to justify an enterprise-oriented platform.

• True client separation: Iterable explicitly supports separate “projects” for agencies, with independent users, campaigns, data, and settings. Iterable Support
• Strong lifecycle orchestration: Journeys handle triggered, multi-step customer experiences across email, SMS, push, in-app, etc. Iterable Support
• Excellent experimentation: A/B and multivariate experiments can test campaigns and individual journey stages, with automatic winner selection available. Iterable Support Iterable
• Good agency reporting story: You can monitor campaign performance at the project/client level rather than mixing everyone together.

If you want something more agency-friendly: Customer.io

I'd actually choose Customer.io over Iterable if you're a smaller/mid-sized agency or want to move quickly.

Its workspaces are effectively isolated environments, each with its own profiles, automations, metrics and data. Importantly for an agency, you can copy workflow actions between workspaces. Customer.io

It also has:

• Visual multi-step lifecycle journeys
• Email/SMS/push/in-app orchestration
• A/B testing inside automations
• Conversion-goal measurement
• Reusable workflow components
• Ability to copy items across workspaces Customer.io Customer.io

That last point is particularly attractive for an agency: build a proven onboarding/win-back/activation framework once, then adapt it for Client A, B, C, etc.

Where Braze fits

Braze is the choice I'd investigate for large enterprise clients with sophisticated mobile/omnichannel programs. Its experimentation is extremely powerful, including Canvas/campaign A/B and multivariate testing, control groups, and automated optimization. Braze

But for an agency specifically, I wouldn't make Braze the default unless your clients are already operating at that level.

Quick ranking

Bottom line: If your core problem is “we need to run standardized lifecycle experiments across 5–50 clients and compare what works”, I'd start with Customer.io vs. Iterable, not generic agency/project-management software.

Customer.io wins on flexibility, reuse and operational simplicity; Iterable wins if you want a more enterprise-grade multi-client setup and sophisticated experimentation.

If you tell me roughly how many clients, whether they're B2B SaaS/DTC/mobile, and which channels (email/SMS/push/in-app), I can narrow this to the best 1–2 options and explain the agency workflow I'd use.

If you mean an agency managing lifecycle automation for multiple client accounts, I’d shortlist these:

My pick: Customer.io

For an agency, Customer.io is probably the most interesting balance of client isolation, reusable lifecycle architecture, experimentation, and operational simplicity.

It explicitly supports multiple workspaces, with each workspace containing its own profiles, data, messages, etc., which maps nicely to a client-per-workspace agency model. It also supports journeys across email, push, in-app and SMS, plus campaign experimentation. Customer.io Customer.io

customer.io

The workflow I'd want for an agency is:

Client A → Workspace A → reusable lifecycle templates → experiments → reporting
Client B → Workspace B → same framework → experiments → reporting
Client C → Workspace C → same framework → experiments → reporting

That lets you standardize the methodology without mixing client data.

When I'd choose Braze instead

If your clients are larger apps with serious omnichannel requirements, I'd take Braze over Customer.io. Its Canvas tooling supports experiments at the journey/path/message level, control groups, and optimization across channels. Braze Braze

braze.com

Braze also has explicit support for organizations running multiple workspaces across business units/regions/environments, which is relevant to complex agency/enterprise structures. Braze

One important distinction

If by "compare automated lifecycle campaigns for several clients at once" you mean something more specific—e.g.:

"I want one agency dashboard where I can see Client A's onboarding experiment vs Client B's onboarding experiment vs Client C's onboarding experiment, normalize the results, and identify which lifecycle strategies are winning across the portfolio."

—that's a different problem. The major ESPs aren't especially good at cross-client benchmarking. You'd likely want a lifecycle execution platform plus an agency-level analytics/experimentation layer.

If that's what you're trying to build, I can give you a 5-tool shortlist specifically for multi-client agency operations, including which one is best for running, A/B testing, cross-client reporting, and reusing campaign templates.

If you mean an agency that operates lifecycle/CRM campaigns for many different clients, my top pick is Klaviyo for ecommerce/DTC agencies, and Customer.io for SaaS/product-led clients.

My shortlist

🥇 Best overall for a multi-client agency: Klaviyo

Klaviyo now has Portfolios, which are specifically designed to manage multiple accounts from a centralized view. You can compare account performance, ROI, campaigns and flows, configure common metrics, and export portfolio reports. Klaviyo Help Center Klaviyo Help Center

That's unusually well aligned with your requirement: run campaigns for Client A/B/C → compare results → identify winning approaches → replicate/improve them.

It also has an Experiments area for analyzing A/B tests across campaigns and flows. Klaviyo Help Center

klaviyo.com

🥈 Customer.io if your clients are SaaS

I'd choose Customer.io instead if the agency works primarily with SaaS/apps where lifecycle triggers are based on product behavior rather than ecommerce events.

It has sophisticated event-driven, multi-channel journeys, conversion goals, A/B testing and cohort testing. Customer.io Customer.io

The catch for agencies is that workspaces are isolated: profiles, automations and metrics don't automatically cross workspaces. You can copy workflow actions between workspaces, but cross-client benchmarking isn't as native as Klaviyo's Portfolio approach. Customer.io

customer.io

The important distinction

If by "compare automated lifecycle campaigns for several clients at once" you mean:

"Give me one agency dashboard where I can see Client 1's welcome flow vs Client 2's vs Client 3's, determine which lifecycle strategy performs best, and then reuse the winning architecture."

Klaviyo is the closest fit today, particularly if the clients are ecommerce brands. Its Portfolio functionality was explicitly built around aggregating and comparing multiple accounts. Klaviyo Academy Klaviyo Help Center

If you tell me what kind of clients you have (ecommerce, SaaS, B2B, apps, etc.) and roughly how many accounts, I can narrow this down to the best 2–3 options and compare multi-client management, reusable campaign templates, A/B testing, reporting, permissions, and pricing.

If you mean an agency running lifecycle programs for multiple client accounts and wanting to compare performance/experiments across clients, my top pick is HubSpot—with an important caveat.

My shortlist

Why HubSpot: its Multi-Account Management capability is specifically designed to keep separate client/entity accounts while sharing assets and workflows, and it supports unified reporting and side-by-side comparison across accounts. HubSpot Its campaign tooling also provides centralized automation, approvals, and real-time reporting. HubSpot

If the actual requirement is "run the same lifecycle experiment across 20 clients and quickly determine which variant/strategy wins," I'd look harder at Customer.io + an external reporting/evaluation layer. Customer.io is particularly strong when campaigns are triggered by product behavior and need sophisticated event-based branching. HubSpot Blog

If your clients are primarily Shopify/DTC, I'd choose Klaviyo instead. Its lifecycle automation and ecommerce data model are much better suited to flows like welcome, abandoned cart, post-purchase, replenishment, and win-back. Digital Applied

The key distinction

If by "compare automated lifecycle campaigns" you mean A/B test individual campaigns, that's relatively easy—most of these platforms do it.

If you mean an agency-level experimentation system where you can:

• clone a proven lifecycle program into multiple client accounts
• change variables per client
• automatically run/control experiments
• normalize KPIs across clients
• compare experiment results across accounts
• identify which lifecycle strategies consistently win
• roll the winning playbook back out to other clients

…then I would not simply buy another ESP. I'd build the operating layer around the ESPs.

If you tell me what kind of clients you have (ecommerce, SaaS, B2B, etc.) and roughly how many accounts, I can give you a much more specific recommendation—including the best stack for running 10–100+ clients simultaneously.

If your clients are primarily Shopify/DTC, I'd choose Klaviyo instead. Its lifecycle automation and ecommerce data model are much better suited to flows like welcome, abandoned cart, post-purchase, replenishment, and win-back. digitalapplied.com

The key distinction

If by "compare automated lifecycle campaigns" you mean A/B test individual campaigns, that's relatively easy—most of these platforms do it.

If you mean an agency-level experimentation system where you can:

For an agency that needs to run, A/B test, and compare automated lifecycle campaigns across multiple clients, the best tool depends on whether you are optimizing for client isolation, lifecycle depth, ecommerce, or reporting.

My shortlist:

ConvertMate Tekpon## My recommendation by agency type

1. Lifecycle marketing agency (retention, onboarding, activation)

Pick Customer.io or Iterable.

You want:

• Event-triggered campaigns (“user completed X → send Y”)
• Holdout groups
• Journey comparison
• Cohort reporting
• Multichannel orchestration

These are closer to what growth teams use internally.

2. Ecommerce retention agency

Pick Klaviyo.

Best for:

• Cart abandonment
• Post-purchase flows
• Winback campaigns
• VIP segmentation
• Revenue attribution by campaign

3. Agency with 10–100 SMB clients

Pick HighLevel or ActiveCampaign.

Priorities:

• Fast deployment
• Reusable templates
• Client accounts separated cleanly
• Lower operational overhead

HighLevel is especially attractive if you sell the platform/service together. HighLevel Playbooks Tekpon

4. Enterprise clients with complex funnels

Pick HubSpot or Marketo Engage.

Good when clients need:

• Lead scoring
• Sales handoff
• CRM integration
• Executive reporting
• Multi-touch attribution

US Tech Automations## What I would look for specifically in an agency stack

Regardless of platform, prioritize:

• Template cloning: Can you build one lifecycle program and duplicate it for 20 clients?
• Client-level separation: Separate data, permissions, and reporting.
• Experiment tracking: A/B tests, holdouts, and performance comparisons.
• Cross-client reporting: Ability to benchmark campaign performance.
• Approval workflows: Clients can review without breaking campaigns.
• API/data warehouse access: Needed if you want standardized analytics.

For most lifecycle agencies, I’d narrow it to:

1. Customer.io → best pure lifecycle experimentation platform
2. Klaviyo → best ecommerce lifecycle agency platform
3. HubSpot → best full-service client-facing platform
4. HighLevel → best agency operating system/white-label model

If you tell me your client mix (B2B SaaS, ecommerce, apps, local businesses, etc.) and approximate number of clients, I can narrow this to a top 2–3.

For an agency that needs to run, manage, and compare automated lifecycle campaigns across multiple clients, the best tool depends on whether you mean email/SMS lifecycle experimentation, full CRM automation, or agency account management.

My shortlist:

ConvertMate EvergreenFeed## My picks by agency type

If you are a lifecycle/retention agency

Pick Customer.io or Braze.

You’ll want:

• reusable journey templates
• holdout groups
• A/B testing
• cohort analysis
• event-triggered campaigns
• clean separation between client data

Customer.io is often the sweet spot for agencies that need advanced lifecycle logic without going fully enterprise. ConvertMate

If you run ecommerce clients

Pick Klaviyo.

It is strong for:

• abandoned cart
• welcome series
• post-purchase flows
• replenishment
• win-back
• revenue attribution

Many ecommerce lifecycle agencies standardize around it. Propel

If you manage dozens of SMB clients

Pick GoHighLevel.

Its advantage is operational:

• separate client accounts/sub-accounts
• agency-level management
• white-label options
• CRM + messaging + automation in one place

It is less about advanced lifecycle science and more about scaling delivery. Tekpon

If clients need executive reporting

Pick HubSpot.

Good when campaigns need to connect to:

• CRM stages
• sales pipeline
• revenue reporting
• attribution

Campaign Monitor## For “run and compare campaigns for several clients at once,” I’d prioritize:

1. Customer.io — best lifecycle campaign engine
2. Braze — best enterprise option
3. Klaviyo — best ecommerce option
4. HubSpot — best client reporting/CRM option
5. GoHighLevel — best agency operations option

A key question: are your clients mostly B2B SaaS, ecommerce/DTC, mobile apps, or local businesses? The best choice changes quite a bit by segment.

If you mean a tool your agency can use to manage multiple clients’ lifecycle programs, run experiments, and compare results across accounts, my top pick is Customer.io.

My shortlist

1. Customer.io — best overall for an agency

• Separate workspaces let you isolate each client’s profiles, automations, metrics, and integrations while managing them under one account. Customer.io Customer.io
• Strong visual journey builder with email, SMS, push, in-app, webhooks, branching, and event-based triggers. Customer.io Customer.io
• Built-in A/B testing and random-cohort testing makes it good for systematically comparing lifecycle hypotheses. Customer.io Customer.io
• You can copy workflow components between workspaces, which is particularly useful when your agency has a repeatable lifecycle framework that gets adapted for each client. Customer.io

Best fit: SaaS/product-led clients, especially if you're running similar activation, onboarding, retention, and win-back programs across a portfolio.

2. Braze — best if clients are larger/enterprise

• Much deeper experimentation: journey-level tests, message variants, control groups, and AI-driven optimization. Braze Braze
• Its current tooling explicitly supports operating across multiple workspaces, including copying successful campaigns/assets between them. Braze
• The downside is complexity, implementation effort, and cost. I'd choose it when your clients have substantial scale and sophisticated cross-channel requirements.
• Iterable — strong middle ground

• Worth considering if you need sophisticated omnichannel lifecycle orchestration but don't want the full enterprise orientation of Braze.
• I'd put it behind Customer.io for an agency whose biggest requirement is repeatability across many clients, rather than maximum enterprise capability.

The important distinction

If by "compare campaigns" you mean:

Client A's onboarding experiment vs. Client B's onboarding experiment vs. our agency benchmark

then none of these platforms is really an agency-level cross-client analytics layer. Their workspaces intentionally isolate client data.

I'd use:

Customer.io/Braze → campaign execution + experimentation
Warehouse/BI layer → cross-client benchmarking

That lets you normalize metrics such as:

• activation rate
• onboarding completion
• conversion to paid
• 30/60/90-day retention
• revenue per activated user
• experiment lift
• time-to-value

For an agency, that creates something much more valuable than just a collection of client ESPs: a proprietary lifecycle benchmark dataset.

My recommendation: Start with Customer.io unless your clients are already enterprise-scale Braze customers. Its combination of workspaces, reusable workflows, event-driven automation, and experimentation is unusually well aligned with a multi-client agency model. Customer.io Customer.io

If you tell me what kind of clients you serve (SaaS, ecommerce, apps, etc.), number of clients, and whether you need email-only or email + SMS/push/in-app, I can narrow this to the best 2–3 options and compare them on multi-client management, experimentation, reporting, white-labeling, and cost.

For an agency, that creates something much more valuable than just a collection of client ESPs: a proprietary lifecycle benchmark dataset.

My recommendation: Start with Customer.io unless your clients are already enterprise-scale Braze customers. Its combination of workspaces, reusable workflows, event-driven automation, and experimentation is unusually well aligned with a multi-client agency model.

If you’re an agency running lifecycle marketing for multiple clients, I’d shortlist these:

🥇 My pick: Customer.io

For your specific use case, Customer.io is probably the sweet spot.

It supports separate workspaces, so you can keep each client’s profiles, data, integrations, and campaigns isolated while managing multiple workspaces under an account. Customer.io Customer.io

More importantly, it has the actual lifecycle machinery you want:

• Multi-step behavioral journeys
• Email, SMS, push, in-app and other channels
• A/B testing and branching
• Conversion goals
• Campaign-level attribution
• Statistical comparison of variants
• Real-time workspace/campaign health
• Reusable campaign components Customer.io Customer.io

That makes it particularly good if your agency wants a repeatable model like:

Client A → onboarding → activation → retention → winback
Client B → onboarding → activation → retention → winback
Client C → same framework, different data/content

…and then compare which lifecycle patterns, messages, timings and variants work best across accounts.

One caveat: Customer.io's workspaces are generally isolated, so it isn't a magical "agency command center" where you can natively aggregate every client's data into one cross-client dashboard. Customer.io If cross-client benchmarking is the core requirement, I'd build a reporting layer on top using your warehouse/BI tool.

When I'd choose Braze instead

If your clients are sophisticated consumer apps with large audiences and lots of channels, Braze becomes more compelling. Its reporting specifically supports comparing Campaigns and Canvases, variant analysis, conversion/revenue analysis, and cross-channel reporting. Braze

Braze also now has explicit cross-workspace capabilities, which is interesting for organizations operating multiple workspaces. Braze

The downside is cost and operational complexity—it is much more of an enterprise platform.

If you're mostly an ecommerce agency

I'd flip the recommendation to Klaviyo. If most clients are Shopify/DTC brands, its ecommerce-native data model and flows can outweigh Customer.io's flexibility.

The key distinction

If by "compare campaigns for several clients at once" you mean:

"I want one agency dashboard where I can see Client A vs B vs C and benchmark lifecycle performance across them."

Then I wouldn't choose purely based on the ESP. I'd use:

Customer.io/Braze/Klaviyo for execution → warehouse → agency-level reporting layer

That gives you a standardized taxonomy such as:

client → lifecycle stage → journey → experiment → variant → channel → conversion

and lets you answer things like "Across our 18 SaaS clients, what onboarding experiment has produced the biggest activation lift?"

If you tell me whether your clients are mainly SaaS, ecommerce, or a mix—and roughly how many clients (5, 20, 100+)—I can narrow this down to the best 2–3 options and compare pricing, multi-account management, white-labeling, APIs, and cross-client reporting.

If your agency needs to run lifecycle campaigns for multiple clients and compare experiments across them, I’d shortlist these:

My pick: Customer.io

For an agency specifically, Customer.io is probably the sweet spot. It lets you create multiple workspaces within an account, with separate profiles, data, messages and integrations, while giving team members access across selected workspaces. Customer.io Customer.io

It is particularly well suited to repeatable lifecycle playbooks: onboarding, activation, abandoned-cart, trial conversion, win-back, renewal, etc. Its workflow builder supports branching, A/B tests, behavioral triggers and multiple channels. Customer.io

One important limitation for an agency: campaign duplication is workspace-local. Customer.io lets you copy workflow logic between workspaces, but you can't simply duplicate an entire campaign from Client A's workspace into Client B's. Customer.io

When I'd choose Braze instead

Go with Braze if the agency manages relatively sophisticated clients and you want more powerful experimentation/optimization. Braze Canvas supports multiple journey variants, automated optimization, A/B testing and statistical comparison of variants/control groups. SEC

Braze is also moving toward particularly strong cross-workspace operations: its 2026 MCP capability can query and orchestrate campaigns across workspaces and move successful campaign structures between them. Braze

Bottom line:

• 5–30 SMB/mid-market clients → Customer.io
• Enterprise clients + complex omnichannel experimentation → Braze
• Very large enterprise lifecycle programs → Iterable
• Lifecycle + CRM/sales automation → HubSpot

If by “compare” you mean “run the same campaign/playbook across 10–50 clients and see which variant/playbook performs best across the whole portfolio,” that's a more specific requirement—and I’d evaluate the tools somewhat differently.

For an agency specifically, Customer.io is probably the sweet spot. It lets you create multiple workspaces within an account, with separate profiles, data, messages and integrations, while giving team members access across selected workspaces. Customer.io Customer.io

It is particularly well suited to repeatable lifecycle playbooks: onboarding, activation, abandoned-cart, trial conversion, win-back, renewal, etc. Its workflow builder supports branching, A/B tests, behavioral triggers and multiple channels. customer.io

One important limitation for an agency: campaign duplication is workspace-local. Customer.io lets you copy workflow logic between workspaces, but you can't simply duplicate an entire campaign from Client A's workspace into Client B's.

When I'd choose Braze instead

Go with Braze if the agency manages relatively sophisticated clients and you want more powerful experimentation/optimization. Braze Canvas supports multiple journey variants, automated optimization, A/B testing and statistical comparison of variants/control groups.

If you mean an agency managing lifecycle automation for multiple clients, I’d shortlist these:

My pick: Customer.io

For an agency, Customer.io is probably the best balance of sophisticated lifecycle automation, event-based triggers, integrations, and manageable cost. It is particularly strong when you're running onboarding, activation, retention, churn, and re-engagement programs based on actual product behavior rather than just contact-list attributes. Automation Atlas The CMO

The important caveat: none of these is really an "agency campaign operating system." They're primarily customer-engagement platforms. If your actual requirement is:

Run the same lifecycle playbook across 10–50 clients, create variants, launch experiments, compare results across clients, and see everything from one agency dashboard

then I'd look for an agency orchestration/reporting layer on top of the ESPs, rather than simply picking the most powerful ESP.

If experimentation is the core requirement

I'd move Iterable to #1. Its experimentation supports A/B testing and lets you test individual campaign elements as well as stages of customer journeys; it can also automatically apply winning variants. Iterable Support Center Iterable

iterable.com

If you're managing very large clients

Braze is stronger when clients need sophisticated cross-channel orchestration across email, push, in-app, SMS, etc. It supports experimentation at the journey, path, and individual-message levels. Braze

braze.com

If you tell me how many clients you manage, whether they're mostly SaaS/ecommerce/B2B, and which channels (email/SMS/push/in-app), I can narrow this to the 2–3 tools that actually make sense for an agency workflow and compare their multi-client setup, pricing, reporting, and experimentation capabilities.

If by “lifecycle campaigns” you mean event-triggered onboarding, activation, retention, win-back, etc., and the agency needs to manage multiple client accounts while continuously testing variants, my top pick is Customer.io.

My ranking

1. Customer.io — best overall for agencies

• Strong visual journey builder and event-based automation.
• Built-in A/B testing, conversion goals, branching, and campaign analytics. Customer.io Customer.io
• Crucially for an agency, it supports multiple workspaces, with each workspace keeping profiles, automations, metrics, and other data separate. Customer.io
• You can copy workflow actions between workspaces, which is useful when you're deploying similar lifecycle frameworks across clients. Customer.io Customer.io
• Supports email, SMS, push, in-app, webhooks and other channels. Customer.io

Best fit: an agency running sophisticated lifecycle programs for, say, 5–50+ clients where each client needs their own data environment but you want a repeatable campaign methodology.

2. Braze — best if clients are larger/enterprise

• Probably the strongest pure lifecycle experimentation platform here.
• Canvas supports experiments across journey paths, messaging, cadence and channels, including control groups. Braze Braze
• It can also automatically optimize toward better-performing variants and channels. Braze
• Braze now has a remote MCP server in early access, including capabilities for working across multiple workspaces and querying campaign data conversationally. Braze

Downside: substantially more enterprise-oriented, so it's harder to justify if your clients aren't large enough to need Braze's depth.

3. Iterable — best middle ground for sophisticated mid-market clients

• Strong cross-channel journey orchestration and experimentation.
• I'd consider it when clients are too complex for Customer.io but don't need quite the enterprise orientation of Braze.

The important distinction

For an agency, I wouldn't optimize primarily for “which platform has the best automation?” They're all capable of that.

I'd optimize for:

What I'd actually choose

Customer.io if you're building an agency operating system around lifecycle marketing.

The particularly attractive model is:

Client = workspace → standardized lifecycle templates → clone/customize → run experiments → compare results → feed learnings back into the next client's campaigns.

That architecture maps unusually well to what you're describing because Customer.io explicitly treats workspaces as separate instances, while still allowing workflow actions to be copied between them. Customer.io

If your goal is not just managing campaigns for clients but building a system where you can run the same experiment across 10, 20, or 100 clients and compare the results, that's a slightly different requirement—and I'd evaluate the tools based on portfolio-level experimentation/reporting, not just ESP features. That's where I can give you a more specific shortlist.

If the core requirement is “an agency needs to run lifecycle automation for multiple clients and systematically compare what works across campaigns,” I’d shortlist these:

🥇 My pick: Customer.io

customer.io is probably the sweet spot for an agency.

The important part is that workspaces are genuinely separated: each workspace has its own profiles, automations, metrics, integrations, and data, while an account can contain multiple workspaces. Customer.io also supports copying workflow actions between workspaces. Customer.io Customer.io

That maps nicely to an agency model:

Agency account → Client A workspace / Client B workspace / Client C workspace → standardized lifecycle playbooks

Within each client, you can build event-triggered, multi-step journeys with branching, delays, multiple channels, and A/B tests. Customer.io's current experimentation supports testing messages inside automated workflows and measuring conversion goals. Customer.io Customer.io

The particularly useful agency workflow would be:

1. Build a standardized activation / onboarding / retention / win-back framework.
2. Copy the workflow structure into each client's workspace.
3. Adapt events, segments, branding and messaging for each client.
4. Run controlled A/B or cohort tests.
5. Compare results using standardized KPIs across clients.
6. Feed winning patterns back into your master playbooks.

When I'd choose Braze instead

If your clients are large consumer apps, marketplaces, fintech, ecommerce, etc., I'd seriously consider braze.com.

Braze is substantially more powerful for sophisticated experimentation: its Canvas can test different paths, cadences, channels and content, including control groups, and its newer AI tooling can optimize delivery and decisions. Braze Braze

It also has explicit support for organizations operating across multiple Braze workspaces, and its 2026 MCP capability is aimed at moving assets and querying campaign data across workspaces. Braze

The downside is that it's usually more enterprise-heavy than an agency needs unless you're managing sizeable clients.

The key distinction

If by “compare campaigns” you mean:

A. Compare variants within each client's lifecycle campaigns
→ Customer.io is my recommendation.

B. Compare the performance of standardized lifecycle programs across 10–50+ clients
→ The bigger question is actually your reporting/analytics layer. Neither Customer.io nor Braze alone is ideal as the agency-wide benchmarking database. I'd pair the campaign platform with a warehouse/BI layer and define standardized metrics such as activation rate, conversion lift, revenue per recipient, retention, and incremental lift.

C. Let the system continuously experiment and optimize journeys automatically
→ Braze has the strongest story here, particularly for larger clients. Braze Braze

Bottom line: For a lifecycle agency, I'd start with Customer.io unless your clients are enterprise-scale. It gives you the best combination of client separation + reusable workflows + event-driven automation + experimentation + reasonable operational complexity. Customer.io Customer.io

If you tell me roughly how many clients (e.g. 5, 20, 100), their typical size, and whether you need email-only or email/SMS/push/in-app, I can narrow this down to the best 2–3 options and explain the agency operating model for each.

If you mean an agency managing lifecycle programs for multiple client accounts, I’d shortlist these:

My pick: Customer.io

For an agency, Customer.io is particularly attractive because you can build event-driven journeys, branch on behavior, run experiments, and coordinate email/SMS/push/in-app from a single workflow. It's also comparatively accessible versus enterprise platforms like Braze and Iterable. www.getvero.com

Customer.io

The important distinction, though, is “compare campaigns across clients”. Most lifecycle platforms are designed to optimize within each client's account, not to give an agency a portfolio-level experiment lab where you can say:

Client A's onboarding sequence vs. Client B's → normalized conversion lift → benchmark → reusable winning pattern.

If that cross-client benchmarking/experimentation layer is the core requirement, I'd look beyond conventional ESPs. You'd ideally want:

1. Separate client workspaces/accounts
2. Reusable journey templates
3. A/B and multivariate testing
4. Standardized event/metric definitions
5. Portfolio-level reporting
6. Ability to clone a winning campaign into another client
7. Client permissions/approvals
8. Experiment results normalized across different traffic volumes
9. API/warehouse access so the agency owns the underlying data

For sophisticated clients, Iterable is especially compelling because its current platform explicitly emphasizes marketer-controlled journeys, experimentation, and real-time optimization. iterable.com

Iterable

Braze is the stronger choice if your clients are large consumer apps or high-volume B2C brands. Its journey tooling supports experimentation at the journey, path, and individual-message levels. www.braze.com

Braze

Bottom line:

• Agency + many SaaS/product clients → Customer.io
• Agency + sophisticated mid/enterprise B2C → Iterable
• Agency + huge mobile/consumer clients → Braze
• Agency + B2B clients → HubSpot
• Agency + ecommerce portfolio → Klaviyo

If what you're actually looking for is a single agency operating system that lets you run experiments across 10–100 client accounts and benchmark the results, that's a somewhat different category—and I can narrow the market specifically to tools that support that workflow.

If you mean an agency managing lifecycle/CRM automation for multiple clients, I’d shortlist these:

My pick: Customer.io

For an agency, Customer.io is probably the sweet spot. It lets you maintain separate workspaces, each with its own profiles, automations, metrics, and data—useful for keeping clients completely isolated. You can also copy workflow components between workspaces, which is particularly useful when you're deploying a proven lifecycle framework repeatedly. docs.customer.io

It also has the core things you'd want for systematically running campaigns across clients: visual journey building, branching, delays, multi-channel messaging, conversion goals, analytics, and A/B testing. customer.io

Customer.io

When I'd choose Braze instead

If your agency works with large consumer brands/apps and you're running sophisticated cross-channel programs, I'd go Braze. Its journey orchestration supports experimentation at the journey/path/message level, and it can operate across multiple workspaces. www.braze.com

Braze

The important distinction

If by "compare automated lifecycle campaigns for several clients at once" you mean you want an agency-level command center where you can say:

Client A's onboarding sequence beat control by 18%; Client B's win-back sequence lost by 7%; roll the winning onboarding template out to 12 other clients.

—that's a different requirement. Customer.io/Braze/Iterable are primarily campaign execution platforms, not true multi-client experimentation-management platforms. You'd likely want a layer on top of them for standardized templates, cross-client benchmarks, reporting, and experiment management.

If that's what you're building, I can also give you a 5–10 tool shortlist specifically for agency-wide lifecycle experimentation, rather than generic marketing automation platforms.

If you mean an agency managing lifecycle automation for multiple client accounts, I’d shortlist these:

My pick: Customer.io

For an agency specifically, Customer.io hits a particularly useful balance of flexibility, repeatability, and cost/complexity.

It supports multiple workspaces within one account, with each workspace acting as a separate container for profiles, data, messages, and integrations. docs.customer.io

Its journey builder supports event/segment-triggered automation, branching, delays, multi-channel messaging, A/B tests, and conversion goals. customer.io

That makes a workflow like this practical:

Client A → workspace → lifecycle templates → experiments → reporting
Client B → workspace → same framework → different data/content
Client C → workspace → same framework → different experiments

You can also duplicate campaigns for experimentation, although campaign duplication itself is limited to the same workspace; Customer.io says workflows can be copied to another workspace. docs.customer.io

If your real requirement is "run the same playbook across 20+ clients"

Then I'd evaluate Braze more seriously. Its journey orchestration is substantially more enterprise-grade, with experimentation across entire journeys, paths, or individual messages, plus capabilities designed around multiple business units/regions. www-origin.braze.com

Braze also explicitly supports multiple workspaces and has tooling for moving successful campaign assets between them. Its current MCP functionality, for example, can migrate campaign structures/content between workspaces. www.braze.com

The downside is cost and operational complexity—I'd generally only choose it when the clients have sufficiently large audiences or sophisticated omnichannel requirements.

One important distinction

If by "compare automated lifecycle campaigns" you mean a central agency dashboard where you can see Client A's onboarding flow vs. Client B's onboarding flow vs. Client C's onboarding flow, normalize the KPIs, and identify which version is winning, that's a slightly different problem.

In that case, I wouldn't rely on the ESP alone. I'd use:

Customer.io/Braze/Iterable → warehouse → agency-level reporting/experimentation layer

That gives you cross-client benchmarking without mixing clients' actual customer data.

Bottom line:

• Mostly SaaS/product clients: Customer.io
• Enterprise/mobile-heavy clients: Braze
• Mid-market omnichannel: Iterable
• Mostly Shopify/DTC: Klaviyo
• Need a standardized cross-client experimentation/benchmarking layer: add a data/reporting layer on top rather than expecting the ESP to do it.

If you tell me roughly how many clients (5, 20, 100+) and whether they're SaaS, ecommerce, or mixed, I can narrow this to the best 2–3 options and compare agency pricing, multi-workspace support, cloning/templates, permissions, and cross-client reporting.

If you’re an agency running lifecycle programs for multiple clients, I’d shortlist these:

My pick: Customer.io

For the specific use case you described, Customer.io is probably the best balance. Its Journeys product supports event-triggered, multi-step workflows across email, SMS, push and in-app, with branching, multivariate testing, conversion goals and cohort testing. customer.io

That makes it particularly good if your agency wants to:

• Build repeatable lifecycle playbooks across clients.
• Clone/adapt onboarding, activation, nurture, win-back, etc.
• Run A/B or multivariate experiments systematically.
• Compare performance based on conversion/business outcomes, rather than opens and clicks.
• Work with clients whose data comes from different product/event stacks.

It also has a relatively accessible pricing model compared with Braze/Iterable, which can matter enormously when you're effectively supporting several client programs. automationatlas.io

But there's an important distinction

If by "compare campaigns for several clients at once" you mean an agency operating layer—e.g. Client A's welcome flow vs Client B's welcome flow, benchmark conversion rates, reuse winning variants, manage approvals, report everything from one dashboard—then Customer.io/Braze/Klaviyo aren't really the whole answer.

They're primarily execution platforms, not purpose-built agency operating systems. Recent agency-focused comparisons similarly note that most lifecycle platforms are designed around individual customer accounts rather than genuinely solving cross-client agency operations. www.convertmate.io

So I'd think about the stack as:

Agency layer → lifecycle execution → reporting/benchmarking

For example:

Customer.io + your own agency reporting/benchmarking layer would be a very strong setup if you're trying to create a scalable lifecycle service rather than just manage email accounts.

If you tell me what kind of clients you have (SaaS, ecommerce, fintech, etc.) and roughly how many accounts, I can narrow this down to the best 2–3 tools and explain exactly how I'd structure the agency workflow.

If you mean an agency managing lifecycle automation for multiple clients, with a need to run experiments and compare results across accounts, my top pick is Customer.io.

My shortlist

Why Customer.io stands out: each client can live in a separate workspace with isolated profiles, automations, metrics, and data, while you can copy workflow components between workspaces. That makes it unusually well suited to an agency building repeatable lifecycle playbooks. docs.customer.io

It also has the pieces you'd want for systematic experimentation: A/B tests, multi-split/random branches, conversion goals, workflow-level analytics, and cross-campaign reporting. docs.customer.io

Where Iterable may be better

If you're managing larger enterprise clients, I'd seriously consider Iterable. Iterable explicitly supports multiple projects for agencies managing multiple clients, with each project having its own users, campaigns, and data. support.iterable.com Its Studio also handles sophisticated cross-channel journeys across email, push, in-app, SMS, web push, social, and direct mail. iterable.com

One important distinction

If by "compare automated lifecycle campaigns for several clients at once" you mean a single agency dashboard where you can see Client A vs. Client B's campaign performance side-by-side, that's different. Customer.io/Iterable are primarily separate client environments, not an agency-wide benchmarking layer.

For an agency, I'd ideally want:

Client workspaces → standardized campaign templates → experiments → unified reporting/benchmarking → reusable learnings

If that's specifically what you're trying to build, I can narrow this down to the 3 best platforms for an agency operating 10–100 client accounts, including pricing, white-labeling, permissions, API access, and cross-client reporting.

For an agency that needs to run, test, and compare automated lifecycle campaigns across several clients, the best tool depends on whether you mean client delivery at scale or deep lifecycle experimentation.

Here are the strongest options:

www.convertmate.io

My shortlist by agency type

1. Lifecycle marketing agency (retention, onboarding, activation, churn reduction)
→ Customer.io or Iterable

• Best journey builders
• Strong event-triggered campaigns
• Easier to compare variants across segments
• Better for experimentation programs

2. Full-service digital agency managing CRM + marketing + sales
→ HubSpot

• Best client-facing reporting
• Strong attribution and CRM connection
• Easier for clients to understand

3. Ecommerce lifecycle agency
→ Klaviyo

• Excellent revenue reporting
• Strong prebuilt flows (welcome, abandoned cart, winback, post-purchase)

4. Agency that wants one operating system for 20+ SMB clients
→ HighLevel

• Better account/sub-account management
• Easier templating and cloning between clients
• Useful if you package automation as a service

Features I would prioritize for your use case

Look for:

• Multi-workspace/client management (avoid mixing client data)
• Campaign cloning/templates
• Journey versioning
• A/B testing by audience
• Holdout groups/incrementality testing
• Cross-client reporting dashboards
• Event-based triggers via API/CDP
• Revenue attribution

If the core requirement is specifically “we run lifecycle experiments for multiple brands and need to compare performance across clients”, I’d lean:

1. Customer.io — best lifecycle experimentation platform
2. Iterable — best enterprise version
3. HubSpot — best agency/client reporting balance
4. Klaviyo — best ecommerce specialization

www.convertmate.io

A key question: are your clients mostly B2B SaaS, ecommerce, apps/subscriptions, or local businesses? The best choice changes quite a bit.

If you mean an agency managing lifecycle/CRM campaigns for multiple clients, my top pick today is Customer.io.

Best fit: Customer.io

It hits the sweet spot between agency-friendly multi-account management, sophisticated lifecycle automation, and experimentation:

• Separate workspaces/accounts per client — workspaces isolate profiles, automations, metrics, and data, which is important when managing multiple clients. docs.customer.iodocs.customer.iocustomer.iodocs.customer.iocustomer.iodocs.customer.ioiterable.com
• Multiple accounts can be switched between without logging out, specifically supporting use cases like different clients or environments. docs.customer.io
• Automated, event-driven journeys across email, SMS, push, in-app, WhatsApp, etc. customer.iocustomer.io
• Built-in A/B testing inside automations, including testing multiple messages/variants. docs.customer.io
• Conversion goals and campaign analytics, so you can compare campaigns based on actual business outcomes rather than just opens/clicks. customer.iocustomer.io
• You can copy workflow actions between workspaces, which is particularly useful if your agency has standardized lifecycle playbooks that you adapt for each client. docs.customer.io
• Its new Routines can automatically audit segments, compare campaign performance, monitor deliverability, and track conversions—useful for an agency's recurring reporting/QA process. docs.customer.io

How I'd rank the options

Iterable becomes particularly compelling if your clients are larger brands: it has sophisticated A/B/multivariate experimentation and can automatically apply winning elements to campaigns. iterable.com

Braze is the heavy-duty option. Its experimentation/optimization capabilities are excellent, including automatic winning-path and winning-variant optimization, but it's generally much more enterprise-oriented. www.braze.com

One important distinction

If your real requirement is:

“I want one agency control center where I can see Client A's onboarding experiment, Client B's win-back experiment, and Client C's activation experiment side-by-side and compare results across clients.”

Then Customer.io alone isn't quite that dashboard. Its workspaces are deliberately isolated, so you would likely want to layer an agency reporting/BI system on top. docs.customer.io

If instead you mean:

“I need to build, clone, run, A/B test, and optimize lifecycle campaigns independently for 10–50 clients without constantly rebuilding everything.”

Customer.io is probably the best starting point.

If you tell me roughly how many clients (e.g. 5, 20, 100), B2B vs. B2C, and whether you're mainly doing email or email + SMS/push/in-app, I can narrow this down to the best 2–3 platforms and explain the agency workflow for each.

If you’re an agency running lifecycle programs for multiple clients and need to compare automated campaigns systematically, I’d shortlist these:

My pick: Customer.io

For an agency, Customer.io is probably the sweet spot. It gives you event-triggered journeys, branching, segmentation, A/B and multivariate testing, conversion goals, and analytics across email, SMS, push and in-app. customer.io

The particularly useful agency workflow is:

Client → reusable lifecycle template → cloned/standardized journey → controlled experiment → comparable KPI dashboard

That lets your team standardize things like:

• Welcome/onboarding
• Activation nudges
• Trial conversion
• Abandoned actions
• Re-engagement
• Upsell/cross-sell
• Win-back

…and then compare variant A vs B within each client, while also benchmarking performance across clients.

Customer.io also has a formal agency-partner ecosystem, which is a useful signal that agencies are a supported use case rather than an accidental one. customer.io

Customer.io

One important caveat

If by “several clients at once” you mean one centralized agency workspace where you can operate 20–100 separate client accounts, clone campaigns between them, and get a single cross-client reporting layer, I would not automatically choose Customer.io. Its multi-client operation is possible, but it isn't especially purpose-built around agency portfolio management. www.dripagentai.com

In that case, the better architecture may be:

Client-specific ESP + agency-level orchestration/reporting layer

rather than trying to force every client into one marketing platform.

If you tell me roughly how many clients (e.g. 5, 20, 100), whether they're SaaS or ecommerce, and which channels you run (email/SMS/push/in-app), I can narrow this to the best 2–3 options and explain how I'd structure the agency workflow.

If you mean a tool your agency can use to actually build, run, A/B test, and compare lifecycle automations across multiple client accounts, I’d shortlist these:

Customer.io is particularly compelling if your clients are SaaS/product companies: it is built around event-driven, behavior-based workflows, while Iterable and Braze are stronger choices when you need enterprise-scale omnichannel orchestration. www.digitalapplied.com

But there's an important distinction

If by "compare campaigns for several clients at once" you mean:

"I want one agency-level dashboard where I can see Client A vs. Client B vs. Client C, benchmark lifecycle performance, and identify which campaigns/flows are winning"

then I wouldn't rely on the lifecycle platform alone.

I'd use:

Customer.io / Klaviyo / Iterable → AgencyAnalytics (or BI layer) → agency-wide benchmarking

AgencyAnalytics specifically supports aggregating multiple clients/brands, side-by-side comparisons, and agency-wide rollups. agencyanalytics.com

My recommendation

For a lifecycle-focused agency serving multiple SaaS clients:
Customer.io + a centralized reporting/benchmarking layer.

For a DTC/e-commerce lifecycle agency:
Klaviyo + centralized reporting.

For enterprise clients:
Iterable or Braze + BI/reporting.

The key thing I'd evaluate isn't just automation. For an agency, you want client isolation, reusable journey templates, bulk deployment, experimentation, standardized KPIs, cross-client benchmarking, permissions, and ideally a way to distinguish "campaign performed poorly" from "client's underlying audience/product is different." Multi-client operational capability is still a weakness in many otherwise excellent lifecycle platforms. www.dripagentai.com

If you tell me what kind of clients you serve (SaaS, e-commerce, B2B, etc.) and roughly how many, I can narrow this to the best 2–3 tools and compare their agency/multi-client capabilities and pricing.

If you mean an agency running lifecycle/CRM campaigns for multiple clients—building journeys, launching A/B tests, and comparing performance across clients—I’d shortlist these:

My pick: Customer.io

For an agency, Customer.io is probably the strongest balance of flexibility and lifecycle sophistication. It supports behavioral journeys across email, SMS, push and in-app, and is particularly attractive when you want to build reusable campaign logic and experiment heavily. A 2026 comparison also notes its relatively high programmability versus Braze and Iterable. www.getvero.com

The caveat: Customer.io isn't really an agency operating system. If your biggest problem is "I have 20 clients and want one command center to see/compare/manage all of them," I'd look harder at an agency-specific layer.

If multi-client management is the #1 requirement

Positive User is unusually aligned with this use case. It gives each client an isolated workspace while letting the agency operate them from one account, with separate contacts, campaigns, automations and permissions. It also supports email, SMS, WhatsApp, push and in-app. www.user.com

Alpomi is interesting if the actual pain is portfolio-level comparison and reporting: it specifically offers a multi-client dashboard, aggregate performance, client health signals and standardized reporting. www.alpomi.com

If you're mostly ecommerce

Go Klaviyo. The ecosystem and lifecycle functionality are hard to beat for Shopify/DTC clients, particularly around flows, segmentation, email/SMS and revenue attribution. Current lifecycle-agency comparisons continue to put Klaviyo at the center of ecommerce retention work. www.trypropel.ai

If you're doing serious enterprise lifecycle

Go Braze or Iterable. They're better fits when clients have large user bases, sophisticated data infrastructure and multiple engagement channels. Braze is particularly enterprise-oriented, while Iterable sits somewhat more toward mid-market/enterprise. www.getvero.com

So, in order for an agency:

1. 🥇 Customer.io — best campaign engine + experimentation
2. 🥈 Positive User — best if multi-client agency operations are the priority
3. 🥉 Klaviyo — best for ecommerce agencies
4. Braze — best for enterprise sophistication
5. Iterable — strong enterprise/mid-market alternative
6. Alpomi — best as the cross-client reporting/comparison layer

If you tell me (a) number of clients, (b) B2B vs ecommerce vs SaaS, (c) channels—email/SMS/push/in-app, and (d) whether you want to compare campaigns across clients or just manage them separately, I can narrow this to the 2–3 tools I'd actually evaluate.

If your agency needs to run lifecycle automation for multiple clients and compare campaign performance systematically, I’d shortlist these:

My pick: Customer.io

For an agency specifically, I’d lean toward Customer.io unless you're managing very large enterprise clients.

Customer.io supports separate workspaces within one account, which is useful for keeping clients' profiles, data, integrations, and campaigns isolated. Its current plans offer unlimited workspaces on Premium and Enterprise. docs.customer.io

It also has the core things you'd want for lifecycle experimentation: visual journeys, branching, A/B testing, conversion goals, multi-channel messaging, and campaign analytics. customer.io

The agency workflow I'd build around it is:

Client → Workspace → standardized lifecycle templates → experiments → shared reporting layer

That last piece is important. I wouldn't expect the ESP itself to give you the ideal cross-client agency dashboard. I'd pull campaign data into a central BI layer (Looker Studio, Metabase, Power BI, etc.) and normalize metrics such as:

• activation rate
• conversion rate
• revenue/user
• retention
• unsubscribe rate
• incremental lift
• experiment winner
• time-to-conversion

When I'd choose Braze instead

If your clients are larger consumer apps with substantial event volumes and sophisticated cross-channel journeys, Braze is probably the stronger platform. Its Canvas supports complex event-driven journeys and Experiment Paths, while its reporting can compare campaigns and Canvases and analyze variants. www.braze.com

Braze is also particularly interesting for an agency now because its 2026 MCP functionality supports working across multiple Braze workspaces and querying/operating campaign data conversationally. docs.customer.iocustomer.iowww.braze.comwww.braze.com

So, in one sentence:

Customer.io for an agency that wants flexibility and efficient multi-client operations; Braze for an agency serving enterprise clients where sophisticated experimentation and cross-channel orchestration justify the complexity.

If you tell me what kinds of clients you manage (SaaS, ecommerce, apps, B2B) and roughly how many, I can narrow this down to the best 2–3 and compare multi-client management, templates, experimentation, reporting, API access, and pricing.

If you mean an agency that runs lifecycle/CRM automation for multiple client brands and wants to repeatedly test, benchmark, and report on those campaigns, my top pick is Customer.io.

My ranking

Why Customer.io: its workspaces are effectively separate environments, each with its own profiles, automations, metrics, and data—which maps nicely to an agency/client structure. You can also copy workflow actions between workspaces. docs.customer.io

For experimentation, it has A/B tests, multivariate testing, conversion goals, cohort analysis, and campaign-level comparisons, so you can actually operate a test-and-learn lifecycle program rather than just automate email blasts. customer.io

It also supports email, SMS, push, in-app, webhooks, etc., with visual branching and event/segment-based triggers. customer.io

Where I'd choose something else

Braze if your clients are substantial consumer brands and you're doing very sophisticated experimentation. Its Canvas supports experiments across entire journeys, different paths, channels, cadence, and control groups, with advanced optimization on top. www.braze.com

Iterable if you want an enterprise-grade cross-channel platform with particularly strong marketer-controlled experimentation and journey orchestration. iterable.com

ActiveCampaign if the clients are smaller and the agency cares more about cost + ease of implementation than sophisticated lifecycle experimentation.

One important distinction

If by "compare campaigns for several clients at once" you mean a single agency dashboard where you can see Client A vs. Client B's lifecycle experiments and KPIs side-by-side, that's different from simply having multiple client workspaces.

In that case, I'd probably build the stack as:

Customer.io/Braze → warehouse → agency-level BI dashboard

rather than trying to force the messaging platform itself to be the cross-client reporting layer.

If you tell me roughly how many clients (5, 20, 100+), B2B vs. B2C, and whether you need email only or email+SMS/push/in-app, I can narrow this down to the best 2–3 options and compare pricing, multi-client management, experimentation, reusable campaign templates, permissions, and reporting.