WAR and PLD will be roughly equals in tanking, both will be useful.

PLD has a silence, on-demand stun, and a shield for a lot of overall damage mitigation.

WAR gets better burst DPS, slightly better AoE damage, Storms Eye which also increases he PLD dmg on the target by 10%, and a short CD short duration mitigation buff every 20 seconds.

For 8 person groups, 1 WAR and 1 PLD will usually be ideal.