Right now there's really not a clear cut number 1 contender. Cain beating Bigfoot doesn't get a shot at the belt imo. Cain vs Werdum would be nice for a clear number 1 contender. (Still don't know how Werdum went from Roy to Russow) Cormier is right up there with a win over Mir for his last SF fight too.
Right now I'd prefer Reem over anyone just for the fireworks it could provide.