Technically WAR should be pulling regardless of composition and a tank swap should happen after the Berserk window.

But if you're just going to do DF stuff then: PLD/WAR = PLD MT, DRK/WAR = DRK MT, WAR/WAR = whichever has better gear is MT, PLD/DRK = imo PLD should MT simply due to part of their threat combo being a part of their DPS rotation which can lead to threat issues with DRK as MT.