I recommend Braintree http://www.braintreepaymentsolutions.com/, having build payment systems on top of paypal payflow pro, paypal express checkout, and Braintree. Their API is far more sane, and their vault system is convenient. Plus they'll let you get your data back out if you ever need to switch. Make sure to ask anyone who would be storing CCNs for you if they have a portability policy. Otherwise, you only get to choose once for the life of your company.

Note: I haven't checked out spreedly yet, but I've heard similarly good things.