Today it's a Gladiator Warrior, tomorrow it's a Balance Priest, next week it's a Frost Shaman. There is no such thing as "highest DPS class". Get over it. Choose whatever you want to choose and make sure YOU are the best you can be.
It's true what the other said, but however it all comes down on what fight and how you execute the fight. There are although simulations, that can give you a brief overview on how top tier players DPS will and would look like without misstakes. You can see them here: DPS Rankings in WoW | PvE - Lvl 100 | 6.0.3 As it looks right now, Glad warrior is pretty insane, topping over 20% overall damage, which means they will have the most DPS output of any class right now. I belive there will be a nerf incomming very soon, atleast before the raids and seasons are released.
