I think their API's are good on their own but in the payments space they are on a completely different level. I've integrated with a number of payment processors (6+) and every single time (without fail) I find myself comparing them to Stripe (unfavorably, for the other processor).

Docs are a mess, API is a mess, web portal is stuck in the 90's, things that are a form on Stripe are an email at best, a call/meeting at worse.

For one processor I had to have 4-5 calls before they would give me a key and let me buy hardware. I doggedly jumped over every barrier, worked with their shit docs, called their terrible API and in the end, <2 weeks before I was going live, found that in production over half my credit cards were failing to be charged. When I asked them about it they said "contact your bank", as if that was a valid response for why 4 of my 6 credit cards threw an error (with no recourse/message).

In <2 week I had Stripe hardware and completely re-wrote the implementation in time for launch.

Stripe is not the cheapest by far, but you'd have to pay me quite a bit of money to consider using anyone else.