Rey Misterio - yes, I think WCW made a big mistake by not giving him the World Title shortly after he lost the mask in 99. I think it would've created huge buzz if he had beaten Flair on Nitro. As for the WWF he's better than most of the options and he'd be a great transition champ for a monster heel.
Christian - no as a heel, maybe as a face, he doesn't have the moveset to be the top heel in the company. He's just too boring. If they turned him face he could pull it off if he kept this character
Edge - yes, only a short reign though. I don't think he's interesting enough and they've jobbed him too much for him to be a convincing long term guy.
Shelton Benjamin - yes, he's been the Raw MVP inring for a few months now and the fans are into him.
Chris Benoit - yes, he's over and they haven't done too much damage to the guy yet.
Chris Jericho - no, he's been damaged beyond repair in the WWF and the fans just won't buy the guy as a main event guy.
Eddy Guerrero - maybe, I think he could work as champion again but I don't think they have the right guys on Smackdown to make him look credible.
Kane - no, he's even more damaged than Jericho. His usefulness was pretty much over after the Shane McMahon feud and then he got stuck with the rapist stuff last year.
Big Show - no, he gets hurt too much.