I have used the Payflow Pro and the Paypal Payments Pro. I found them easy to use from an API standpoint, although Payflow's php API worked well, it required a recompile of php and that meant less ease for patching our servers. After the server setup each was equally okay. The biggest drawback to using the Paypal products was the customer support and set up. Setup was a nightmare and the "salesman"/account rep that we dealt with was less than helpful.
