With respect the UFC main events, this is easily one of the biggest toss ups in awhile but for all the wrong reasons. This isn't a case of who really has the better grappling or striking or is tougher, but who'll find a way to lose in this moment?
Bisping'll beat the breaks off any gatekeeper or mid-tier level fighter the UFC can possibly throw at him. Against your Elvis Sinosic's and Dan Miller's of the MMA world, he'll win every time. Throughout his entire tenure in the UFC, he's beaten only one Top 10 fighter which speaks volumes. There's a certain level of fighter he just can't get past. Broken down, war torn Wanderlei Silva that's only won 3 fights in 7 years? Can't do it. Even the likes of Jorge Rivera? Needed an illegal knee to get the job done. This simply isn't the type of fight he wins.
Vitor Belfort is an incredibly fun fighter to watch with knockout power that is not to be trifled with. However, his record is marred with inconsistencies just the same, but the ceiling he's reached throughout his career has always been much higher. There isn't a single fighter he lost to that wouldn't have finished Bisping (at their ages then). While the majority of his inconsistencies could be traced to the disappearance of his sister, Belfort still unfortunately proved that he's a mental midget against Anderson Silva. Losing to someone of that caliber is nothing to laugh at, but it was how he lost: He literally froze. After exhibiting excellent movement and intelligent aggression, he suddenly stopped moving, allowing Anderson to measure him perfectly for the KO.
Prediction: Vitor Belfort. A vital part of being able to defeat him requires either putting him on his back or keeping him at bay because he respects your power. That isn't a factor here. I think this goes quite similar to Wanderlei/Bisping: Bisping will get hurt, nearly crap his pants, and will be crippled with fear to the point he'll be unable to snag the W. Except when Vitor hurts you, he finishes you.