This may be wrong since I have not seen enough of Dubinsky to get a proper opinion of him but if I'm looking at five years from now, I think i'd take Bolland out of those four. While I don't think he has much chances at becoming a star player, he's likely to be the kind of player that'll do good no matter on which line he plays. He's a great player to have on any depth chart. Again, keep in mind that I'm not including Dubinsky in this, but then again, I might still go with Bolland since I think he'll be that useful.
Grabovski may become awesome in some aspects of the game but he'll need a specific system and complementary linemates to be of any use to a team. I see him as a slightly less skilled Afinogenov, good for secondary scoring and the news' highlight reel.
Bourret just has too many question marks; he might turn out good in the end but I wouldn't bet the farm on it so I'm not entirely surprised that Atlanta traded him for an established player.