The enmity argument is pointless when both tanks can hold more than enough to ensure DPS or healers do not take hate from them.

As for the 2 tanks competing with each other - it's called communication.

PLD is simple, straightforward, and most importantly it is safe. It is far more defensive than WAR and also more difficult to screw up on. WAR has greater potential than PLD, but also requires more from the player.

Going into an encounter where you are very familiar with the content already and have a strategy worked out, WAR will excel. For progression pushes, though, the safety net of PLD is very desirable.