I've used both stripe and braintree to build payment processing services that do hundreds of thousands of dollars in transactions per month.

I can't really tell you which is better because it really does depend on a lot of variables that may be unique to your business (e.g., where you intend to operate, the payment methods your target customer base is comfortable using -- hint: it's not always credit cards and paypal, how you intend to bill).

Since I've got more experience with braintree, though, I can comment on some aspects of its use specifically -- primarily their drop-in UI, which has frustrated me at every turn. Their drop-in is probably one of the most frustrating pieces of technology I've ever integrated into a website. Not because it's poor, necessarily, but because it only feels about 80% complete. The user experience is really frustrating at times. Some examples:

* Last I checked, payment method removal wasn't possible in the drop in - you have to integrate their API specifically for that.

* Choosing what payment method you want can be really confusing due to the card number / email address obfuscation they use in the drop in. For example, if you have two paypal accounts, selecting between one of the other is difficult when they're listed as p----@paypal.com and p----@paypal.com. The same thing happens if you use multiple credit cards of the same issuer (two Visas for example). Simply allowing the user to set a card name in the ui (e.g. "Personal Visa" vs "Work Visa") would mitigate this problem.

* It currently isn't possible to set a Coinbase account as the default payment method in the Drop-in. Despite the Drop-in supporting Coinbase fully in every other way. So there's another reason to incorporate the API.

* Lack of other major payment methods. With BrainTree you get Venmo, Coinbase, CC, Apple/Android pay, and Paypal. Depending on your customer base, you could be woefully under-serving them. As my current business grows, we're now looking into incorporating other processors to use alongside braintree to support things like gift cards, ACH transfers, Amazon Payments, etc. This may just be unique to my industry, but I can't stress enough to do your homework ahead of time and understand how your customers expect to pay you.

* I get numerous reports from users of being unable to pay using paypal through the drop-in if they don't have a credit card attached to the paypal account. I've contacted BrainTree numerous times about this and have yet to get a definitive answer as to why this is the case. Additionally, if a credit card is connected to the paypal account, the withdrawal comes from that and not the paypal balance. If you want to frustrate your user base, let them use their paypal account but not their paypal balance...

As I've typed this, I realized it's a pretty ranty indictment of BrainTree. On the whole it isn't a terrible service. Uptime is good, money goes in, comes out, and my business keeps on running. It's not a bad service, I just have a lot of drop-in frustration. I kind of hope I get a reply that says, "The BrainTree drop-in does all this, you're just using it incorrectly."