We're using Braintree here at Loggly, and like it quite a lot. The API has a neat little Python library that we use on our backend, and is pretty well documented.
The indirection involved in posting billing forms to them means you wind up doing some interesting gymnastics if you want to include a billing form as part of a larger user signup form. You may want to check the JS on our paid signup page -- go to https://www.loggly.com/register/#woodpecker do an inspect element on the submit button, and expand the inline script a few lines down. The script creates an (unfunded, inactive) user on the server, receives a token pointing to this user to use in posting to braintree, and then posts the braintree form.
The indirection involved in posting billing forms to them means you wind up doing some interesting gymnastics if you want to include a billing form as part of a larger user signup form. You may want to check the JS on our paid signup page -- go to https://www.loggly.com/register/#woodpecker do an inspect element on the submit button, and expand the inline script a few lines down. The script creates an (unfunded, inactive) user on the server, receives a token pointing to this user to use in posting to braintree, and then posts the braintree form.