Pfff, I think Thing has the popularity-edge here. But if we look at the facts, Colossus has the edge.
He's stronger (not that much, but still, stronger is stronger) and more durable. He trains on an almost daily basis in the Danger Room, together with Wolverine. Brawling only will get you so far. Fine tuning your skills will get you further in my opinion.
I like'em both, and Thing is going to put up one hell of a fight (and bore us probably with "Don't mess with one of the Yancy Street guys "- like everyone of Yancy Street has two black belts...), but since Colossus is probably faster and certainly stronger and more durable, I vote for Colossus.
I think it's not far fetched to vote for him. Colossus has a Royal Flush, Thing "only" a Straight Flush. Now you can all place your bets 😉