Disclaimer: I now work at Stripe but the following was purely when I used them as a user: Stripe targeted developers from day one and made it extremely simple

Disclaimer: I now work at Stripe but the following was purely when I used them as a user: Stripe targeted developers from day one and made it extremely simple to get up and running (literally seven lines of code for a working payments system) and they documented their api very well. Then they added on a lot of stuff that made me (as a user) happy, like paying out to my bank account a lot more quickly than the competition, adding recurring subscriptions with a few more lines of code etc. Basically, their systems just worked out of the box and were more polished than others that I used.