Tier 1:
These are the current top-level decks in Hearthstone ranked play. They are the closest to optimized or have such ridiculously powerful combos and synergy that they overwhelm the competition. Consequently, losing to these decks often feels "unfair" or "overpowered" because of how much more efficient and sometimes forgiving the deck can be. Play these decks with the understanding that you probably should be avoiding the friend request you get after winning.