Sudden change of no ban system in the groups made for some really one-sided match ups. Much as I hate to say it I think I agree with Reynad, running Shaman, Warrior, Paladin, or Druid in the groups is a bad idea. All of those decks can win against anything, but they aren't particularly favored. Whereas Mage, Warlock, Hunter, Rogue have clear strengths and weaknesses, so running two of them in combination should give you a slight edge.
I'm leaving Priest out because it is such a wild card. Amaz's "Leasher" deck that he ran when Zoo was more than half the ladder has some ridiculous win rate vs agro, like over 90%. But Kibler Priest is a coin flip vs agro and slightly favored in most control match ups. Priest, more than any other class I think, is good or bad in a match up solely based on the list.