I'd suggest Pineapple Payments. They are a new company based upon the CardConnect platform, which was just acquired by FirstData.

FirstData is one of the primary companies in the market, and the rates you get from Pineapple are "interchange optimized". Means you pay 2.9% for AMEX, but ~1.5% for VISA, Discover, etc.

For B2B and even B2C, it's a fantastic savings if you're willing to do just a tiny bit more legwork than Stripe requires.