Here we go again..

[remanz]

Come to think of it every classes have their OP days. From I can remember

Warriors = now
DK = upon LK release. Blood DK ruled arena for like 2 seasons.
Paladin = once a upon time, Seal of Command procs extra swing. Paladin can kill within HOJ stun. Bubble only reduce attack speed by 50%, not damage.
Hunter = now
Mage = Frost mage in Cata. Still today. I think it is BS mage can proc frost damage from another mage's freeze/nova.
Warlock = The end of LK with Shadow Fury and insane survival.
Rogue = can't think of when Rogues are OP.
Priest = The end of LK with disc healing. and Spriest super damage + mana drain.
Shaman = elemental was god in BC days. I was able to stand there just cast LB against a warrior. and let the warrior interrupt me all he wants. I would kill him with 50% hp left.
Druid = the end of LK, blizzard buffed bleed damage. Feral druid was doing crazy amount of damage in arena. They were getting 5 combo points. Instant cyclone. let energy get full. Burst down after cyclone expires.
MONK = yet to been seen