PLDs are better main tanks for their overall survivability. Shield Oath and the cooldowns make up for a better EHP. The PLD can also Stoneskin itself when needed.

WAR is generally a better off-tank. Warrior has better dps potential and also adds nice debuffs such as Storm's Eye and Path that help both the MT as the dps. War can also hold packs of mobs better with Overpower and Flashes; the PLD often has it hard keeping enmity on packs of mobs when they run low on mp.

On coils you ideally want to have both, at least on T13. On earlier coils a good group may run double warriors for increased damage and debuff uptime though.