I've used Braintree for about 5 years. They've always been excellent to work with. I know a couple of other customers of theirs, and all have had good things to say about them.

I've also used Stripe for billing (more recently), and they've been great as well.

If I were starting a new project that required billing, I would absolutely be looking at both Braintree and Stripe. Anyone who doesn't is doing themselves and their business a disservice.