All the opportunities mentioned work. I would chose only one to promote. But you have to be consistent and determined to make it pay off.
Joining all or 3-4 programs is a BIG mistake. Once you decide be sure to read T.O.S. thoroughly, read the fine print, ask questions quickly, Send email to support just to see how quickly they respond.
Clickbank is the easiest just be careful which affiliate program you decide to join.
If they have forum join and ask more questions on how to succeed.
Paul