Authorize is my choice. Don't use them directly-- set up your own UI.

Though, from a "millionaire" point of view you shouldn't be accepting CC for medium/large marketing jobs to begin with. Any firm with authority should be able to have a "check, money order, or transfer" policy. There are too many reasons not to do credit card.

Anyway-- if you'd like some more advice regarding how to take your firm to the next level, let me know and set up a call.