Looking at each character individually...
-Why would Christian win the belt when he's already feuding with the US Champion? He's gonna be busy with the secondary title holder for the next few months, so why would they bother putting MITB on him?
-Seems like WWE realized that Sheamus isn't a main eventer, or at least we can hope. He's simply not good enough. Period.
-Randy Orton has nothing going on at the moment outside of being annoyed by Bryan every week while the focus is completely away from him... maybe that's a sign that he's going to be all "surprise mothafucka" and win the briefcase as there's not much else for him to do, but don't put your money on him.
-Kane... no. RVD would love the briefcase since it's sturdy enough to keep the drug dogs out AND comes with free rolling papers.
-Daniel Bryan has an inferiority complex at the moment, and if he cashes in MITB it's a sure-fire heel turn since he won the belt via flukish means and would get a really big head about it. Have went on and on about how scared I am of that. It's almost a disservice to him, since winning his first WWE Title cleanly over a top guy WITH the weak link storyline would be freaking amazing storytelling. If you can fantasy-book it right, go ahead and fantasy-book Bryan to win, I'm just too skeptical to do it. Either way WWE has to capitalize on Bryan's momentum and they have to do it now.
-So I'll go with CM Punk. Punk's story right now is that he has to validate not needing Heyman, and winning the MITB will do that. And him already having several months of a feud set up will keep him from being booked horribly with the briefcase, so he's the best option imo.