Im not sure what you are charging for or what your business is, but beware that Braintree routinely turns down businesses that their underwriter considers 'risky'. MANY Web2.0 businesses fall into this category. Social networking, some SaaS, online dating, etc.
You may have to shop around to find a payment solution that fits your business. Just a heads up.
They offer everything the big dogs do, but their staff is incredibly helpful and attentive. We use them on FamSpam and GitHub.
I wouldn't find the merchant with the lowest rates, find the one you like the most. As your business grows, you can always renegotiate your rates.