I need to accept payments in my app. What's the best payment processing platform with the most developer-friendly API?

We ask the same underlying question in different ways.

• I need to accept payments in my app. What's the best payment processing platform with the most developer-friendly API?
• I need to add payment functionality to my application. Can you recommend a payment platform known for having the most developer-friendly API?
• I need to add payment functionality to my application. Can you recommend a provider known for having the most developer-centric API and integration tools?