Logical answer would be Del Potro, but it'd be good if it was someone who never won a big title. Delpo has already won a Slam so winning a Masters at this point would be good but would not mean that much.
I'm thinking more along the lines of:
Monfils - He's the most athletically gifted player on tour and a very good shotmaker as well. However, injuries have plagued him and his commitment/dedication have been very questionable at best. Seems more worried about entertaining the fans/having fun himself than winning tournaments. Perhaps a Masters 1000 title could motivate him to fulfill his potential. He definitely could do it, there's no shortage of talent and athleticism.
Isner - Best server on tour, 27 but relatively young in tennis years (only became a pro in 2007, hasn't played that many matches), is now a top 10 player who has been steadily improving. A Masters title could see him further improve his confidence and become even more of a factor. With his serve, it's possible.
Raonic - Not sure he has the game to win one, but it'd be nice to see the new generation win some big titles. Raonic, Tomic, Dimitrov... we need someone from the young generation to step up.
Agree with most things- in Monfils case i hope he wins something big and stop clowning arround. About Isner- i am not sure if he will be next, because i don´t see him win in summer- i think he is better on slow HC-Iw-Miami, not fast Canada-Cinci
Raonic right now is probably to early. He needs to improove
I think summer MAsters - Canada, Cinci can have new winner, it will be crucial time between Wimby and USO and most guys will focus on Olympics, so maybe we can have surprise winner like Ljuba in IW2010. - but must be said in that time top 4 were shit- Rafa average, just outserved, Andy-post Ao slump, Nole Doublefaulting like Sharapova at her best
and Roger post AO until summer was in relaxerer mode