I like to think of it more as "if I had to lose an ability/weaponskill, which would I choose?"

PLD - Clemency. I was tempted to pick Cover, but Cover's effect is unique, which could potentially be game-changing if an encounter accommodated it.

DRK - Abyssal Drain. Redundant with Unleash, and, if I had to pick one, I would rather have Unleash.

WAR - Fracture. Very slight DPS gain. Certainly not useless, but I wouldn't miss it.