Lots of variables to consider. Are headbutts allowed or not? During which Vitor "prime" are we talking about?
Is this during Mark Coleman's three-fight losing streak in the UFC, or the period right before that in the UFC or right after in PRIDE when he won the 2000 Grand Prix?
Vitor was my favorite fighter back then, but under most circumstances, I have to go with Coleman.
Vitor was simply beaten too often by wrestlers who repeatedly put him on his back and wore him down. Obviously there are the fights against Couture, but even the much smaller Sakuraba defeated him.
On the flip side, a Pedro Rizzo in his prime won a very close fight (split decision) over a Coleman who didn't have headbutts and was arguably not at his best.
Rizzo was bigger and stronger than Vitor, had much better wrestling and takedown defense, and the brutal leg kicks that Vitor lacked. And while Rizzo's cardio wasn't great, it was significantly better than Belfort's.