I would say CJ and Linkshare. Don't touch the Clickbank stuff. It's because I use merchants you're likely to see at your local mall which Clickbank doesn't have. It depends what kind of affiliate marketing you're doing.
ClickBank rocks my world! They pay a higher percentage and I've recieved checks from them already. I've played with CJ and Linkshare before and what trustno1 said about the merchants is popular at your local mall is right but remember if they go to the mall then why do they need you. But hey I'm not disin' CJ or Linkshare its just my opinion. Do whatever you want but I'm clickin' with ClickBank.