The OP concept is pretty much relative.
I believe that on Bludrutbrawl, any class that have a nuke(obviously) or a good AoE attack is a OP class.
I would say:
-Warrior
-Berserker(Got nerfed a long time ago)
-Blood Ancient
-Legendary Hero
-Enforcer
-Jouster
-Necromancer
There may be more classes, but I don't have experience with then