Having played all the tanks since 5.1, I can say that DRK and PLD feel like the best picks at the moment in feast, they provide an instant shield, aoe mitigation and good debuffs on the enemy team. I feel WAR could be placed on the same level if they were to change nascent flash, one idea is to provide a small shield like its pve counterpart, or have an excog like effect when the targets hp drops below a certain % and maintain a hp return from dealing damage. WAR would feel just as good as DRK and PLD if they made a change to nascent flash, I haven’t tried out GNB much but their shield is also weaker, and they lack a strong debuff like what DRK and PLD have.