both work but if you want API access because you don't want to setup campaigns manually. I mean who does these days?
Remember smartlead does not provide API access at smaller base plans. Instantly does.
the api gap is real but it depends what you're building. instantly gives you access on lower tiers so you can test integrations early. smartlead gates it behind pro but their webhook setup is more flexible once you're actually scaling volume. i'd start with instantly if you just need to validate the workflow, migrate later if you outgrow it
I've mostly used Instantly API, they now have an MCP and its easy to use with Claude to setup campaings and upload leads - able to do it on a granular level too
yeah instantly at $97 25k emails. is pretty good. if one needs more for a client then good problem to have. they want to test more and thus we can get further