If you want to win, play the top 3 classes: Mage, Paladin, and Rogue. Mage's hero power lets you win in the late game (if you are lucky you will be able to pick enough removals to let you play off the board), Rogue is a great tempo class, you either go aggro or flip the board with huge cards like Backstab or SI-7 agent/Undercity Valient, Paladin isn't as consistent, but it's cards are just overpowered.
The shitty classes like Priest and Hunter are just not good. Warrior, Warlock, and Shaman are inconsistent because they rely heavily on the draft, rather than the hero power like the top 3 classes. I'm just bad with Druid so I can't give you advice there.
