If we are taking about Stripe, we should mention the silent competitor barely anyone talks or knows about outside the payments industry: Adyen. Stripe’s current, (private) valuation is $36B. Developers love them. Adyen’s current, public valuation is $43B (they IPO’d amongst little press coverage). Most developers don’t know about them. So what is the difference? Market strategy. Adyen only goes after large businesses…
That hasn't been our experience at all. In our case (a few years back, they might've improved in the meantime) Adyen experience was pretty lousy. Not especially bad, but average - considering many payment gateway APIs were as bad.
In contrast, Stripe was (at the same time, and continues to this day) miles ahead, a pure developer delight. Properly documented, with working API wrappers, working examples, correct API responses. It just worked as expected and was easy to understand.
Unfortunately I don't recall specifics with Adyen as it was a while back, but I know we were pretty unhappy with it. To this day I've never looked at it again, while I recommend Stripe to anyone in position to use it.