This has probably been stated several times by now, but the amazon documentation is absolutely horrible. Braintree, Stripe, and Paypal all have fantastic tech and reliable services in addition to fantastic documentation. I don't have an opinion for any other payment-processing vendors.
Now for the war story: Business was focused on deploying amazon-payments because of the cheap fees. In order to change their minds, I had them call into tech support. After 3 hours and 5 hangups, business opted for another vendor. The implementation was effortless and only took me a few hours.
> Braintree, Stripe, and Paypal all have fantastic tech and reliable services in addition to fantastic documentation.
Paypal sucks for merchants. You're basically at their whim without any legal recourse. Just see what happened to Wikileaks or hundreds of merchants having their accounts frozen and their funds locked without any real reason!
PayPal isn't really that bad. Most of the horror stories are from people breaking the terms of service (donations without getting approval, long preorders etc). Wikileaks was blocked by MasterCard.
We've been in PayPals sights a few times (we had a site bug once that double-charged a bunch of customers, and charged one customer 28 times! We had to do over 1000 chargebacks.) We got a massive rolling hold but the whole time PayPal were willing to talk to us. We've even won some customer card chargeback disputes on digital goods through PayPal.
For a short while we switched to a traditional merchant account but that was hell from day one. Aside from the paperwork to get set up, they hated the fact that 40% of our sales were outside the U.S., that our sales are highly seasonal, etc.
That said, to someone starting today, I'd still probably recommend Stripe instead.
Now for the war story: Business was focused on deploying amazon-payments because of the cheap fees. In order to change their minds, I had them call into tech support. After 3 hours and 5 hangups, business opted for another vendor. The implementation was effortless and only took me a few hours.