We are considering Braintree and Authorize.net's ARB. Another option is PayPal's Website Payments Pro gateway service. Here is a comparison of the two:
PayPal Website Payments Pro w/Recurring Payments: Discount Rate: 2.9% $0-3k; 2.5% $3k-10k; 2.2% 10k+ Transaction Fee: $0.30 Monthly Fee: $30/mo Recurring Billing Fee: $30/mo Monthly Minimum: $0
Braintree: Discount Rate: 2.29% qualified; 2.89% non-qualified Transaction Fee: $0.30 Monthly Fee: $35/mo Recurring Billing Fee: $0.10/transaction + $20/mo and $0.01/card for the Vault service Monthly Minimum: $75 (does not include monthly fee)