I've only seen a few of these (Querrey, Young, Tsonga, Korolev). I really like all four aside from Young (just not impressed with him yet, although it's wonderful he can add a different side to the game).
Tsonga to me SHOULD have the most potential. He has the serve, forehand, volleys, his backhand is pretty good, and he has great movement for a big guy. But his brain, like most other Frenchies, is terrible. Love his game, attitude, style, but he's so frail mentally when he gets against slight opposition. If he can improve that side of him he should be pretty good.
Same goes for Korolev, who would be my #2 pick. He has an explosive game as well, and I could easily see him in the top 10 with some more consistency. His game is already better than Tursunov's I think, but he's still raw and needs experience. And just as a btw, his match against Melzer in the LV SF was one of the best matches all year.
I've only seen him a little bit since then, and it's obvious consistency is not his strength. Hope he can work that out.
Querrey, eh, don't have much to say about him, but he should be a top 15/10 player for most of his career. Should. I wish him the best though.