In Defiance, there is literally no contest, WAR is hands down the hardest tank to kill in this game right now.

This much mitigation is rarely needed, but I did test on a dummy just for curiosity's sake.

You can literally daisy chain CDs together, pairing Awareness with RI, Conva with Thrill, and Rampart/ Vengeance on their own, filling in gaps in between with IB or infuriate - IB, indefinitely, forever. If a WAR wanted to, he/she could sit in defiance and pop cooldowns forever and never not be covered by something, even for a second.