Usually it's WAR > DRK > PLD
Enmity is directly tied to damage (1 damage = 1 enmity, unless skill has multiplier eg. Onslaught has 10) you make as well as WAR has tools like Unchained, highest damage potential and enmity tools like Onslaught with high enmity multipliers. Warrior is natural aggro generating machine and does is most feasibly.

DRK has DA Power Slash which generates more enmity than anything else (4840 aggro potency vs. Butcher 2100 and Rage 1890) in this game as well as DA Plunge and Dark Passenger which too are no way or shape bad now.

PLD on the other hand is the lackluster here. Circle of Scorn and Shield Swipe are very weak oGCD enmity tools (espesially latter because damage was nerfed but aggro wasn't buffed) and Rage of Halone is by far both weakest aggro combo out of 3 and punishes user far more than WAR using Butcher or DRK using Power.