Nonnne of those APIs have anything to do with each other? 4 completely different markets / products.
I've worked with Stripe, Twilio and Google Maps (I prefer Apple Music...) Stripes documentation is always the best. Google APIs are very powerful but often hard to read and I'm neutral on Twilio. The documentation is good and its a good service.
Stripe and Twilio would probably be my favorite of the 3 I've used.
AWS services are hard to use but powerful (same as google is). Mailgun was a powerful API but to many versions of it made it hard to find the right documentation.
Firebase Angular JS 1.x was easy to use. Firebase Angular 2+ I still struggle with sometimes - again, another case of Google APIs being difficult to read.