I want all the layers of the pyramid, eventually, but the top layers matter the most. I can't count the number of times my paranoid "make sure that customers can successfully pay us" end to end test suite has prevented the money faucet from being shut off. I install one perennially at any company I work at and they always pay for themselves surprisingly quickly.

I’ve been involved in B2B (so no payment flow). But it’s basically the same with an handful of integration tests for common workflows. They run fast and mostly serve a canary to ensure that we are not crippling some use cases. When a bug hits us, a test case is added/modified for it.

They’re mostly a reflection of the current requirement of the project.