I currently use Clickbank and E-Junkie. And I've made the mistake of using PayDotCom before.
* If you're not into attracting affiliates and just wanted a secure download solution, use E-Junkie.
* Clickbank is the ONLY way to go if you want any kind of active affiliate volume for your digital DL products (ebooks, ecourses, certain software, etc). Don't expect affiliates to come running as soon as you list your product(s), though. Affiliate recruitment on Clickbank is an art and science all on its own.
* Use PayDotCom if you want dozens of scammers that have found out how to game PDC's already piss-poor system to jump on you and make your life hell trying to sort out who's legitimately selling your product from who's scamming you out of fake commissions.
* Also take a look at
Click2Sell Affiliate Marketing Network - Innovative Affiliate Network Online!, which is the closest actual Clickbank rival there is. The active affiliate base is much, much smaller but there seems to be a much higher concentration of very good, very professional affiliates as well. Snag 8 or 10 (sometimes even less!) of those guys, treat them well, and you'll be well on your way.
As far as setting up an affiliate program account for you, I'll do it but it is NOT going to be free (but it will be done right).