Weidman for sure.
He is still relativelly new to MMA, and in his 9th pro fight his name pops up in the same sentence as other big names. And he is fighting one of the TOP 6-8 guys in the division.
Weidman seems to be a talent, and when i say this i'm reffering to the fact that he seems to learn at a fast pace. With one year BJJ experience under his belt he had a great performance against Galvao at the 2009 ADCC.
He seems to be the kind of guy who absorbs knowledge at a really fast pace and implements it in his fighting style right away.
His striking still represents a big X factor and something he needs to work on imo, but he has time to develop it.
I think he would be a big threat to Silva on the ground. His size + wrestling skills + grappling would create a very dangerous combo for Silva.
Only thing is: how would he be able to get past Spider's hands/striking in the begining and take the fight to the ground?!
I still say: Weidman - MW Champ by the end of 2013.