Reading through this I'm a little surprised by the answers, I would have imagined that it would be WAR because Berserk + Unchained + Internal Release then Butchers Block a couple times generates insane enmity and I would think a DRK spamming Power Slash will find themselves out of MP and out of Darkside before even their Dark Arts Power Slashes would overcome the WARs aggro, and I wouldn't necessarily count PLD out either as DRK needs to use their MP regen combo occasionally and a good WAR will be using Storms Eye to help generate aggro from the Slashing resistance down debuff and attack up where as a PLD generating aggro never needs to use anything other than Rage of Halone.
Having said that I still think a WAR will out aggro the other 2

AOE is a little more interesting tho. In particularly big pulls a WARs Overpower may be unable to hit all the enemies and Steel Cyclone is locked behind their Wrath mechanic. Which makes it a race between PLD and DRK in AOE, PLD has enhanced Flash and the Circle of Scorn DOT on a very short CD, where as DRK has Unleash, Dark Passenger and Salted Earth. Dark Passenger suffers from the same issue as Overpower in particularly large pulls where the mobs surround you so they can attack you, Salted earth is a Fire arrow like DOT I believe and Unleash is Flash with a damage dealing mechanic.
In an AOE aggro war between the two of them I believe it would be which ones MP holds out longer and Im not sure who that would be as DRK has Blood Price but is constantly losing MP to Darkside and Dark Passenger has an MP cost despite being a cooldown while a PLD can use Circle of Scorn without losing MP but has no way of reneging MP without switching to a single target for riot blade and I read somewhere that Flash generates more enmity than Unleash but that could be wrong