Here's what I think of each player there and their potential.
Korolev - can be a very good player but has been dissapointing so far. Maybe Top 50-30
Gulbis - has got the talent, but keeos facing better opponents early on in tournaments, and chokes a lot. If he can be more consistent I think Top 20.
Bolelli - will be Top 30 some time. Good player, not amazing.
Troicki - will be Top 20 in the future. He can be very dangerous, but is dissapointing at times.
Haase - has dropped out of the top 100.
injured? I think he can become a Top 40-30 player.
Cilic - might be Top 10 his year. He is living up to his talent.
Del Potro - has an extremely good chance of gaetting into the top 5 after Wimbledon. Depends on how Davydenko and Roddick do. He, IMO can't get any better than what he is right now.
Querrey - IMO, can be Top 20 material. He just needs to be a bit more consistent and get to 4th round and quarter finals of the Grand slams.
Nishikori - Has a very good chance of making top 30 this year. If he becomes better, maybe top 20-10.
Stakhovky - is a good player. I don't think he can do any better than Top 50-40 though. If he improves a lot, then maybe top 40-25.
That's what I think they can all do. This is based on their skill so far. I could be miles of on some players. For all I know Korolev will be top 20 next year.
Here comes Evgeny!!
Anyway I pick Group 2.