Braintree isn't a bad choice, not the best but better than most. Their documentation and needs for more complex stratiges for domain logic is lacking. Stripe has one of the best documentations I've seen as far as payment gateways go and how it can fulfill most business needs. As far as MVP products go I grade each api on documentation and flexibility. 1. Stripe, 2. Braintree, 3. Custom gatwate solutions such as shopifies gem. Im sure there are many more solutions but as a developer without a huge background in payment processing solutions this is my assessment.