I'm working on a Willpower Tank right now, a weird labor of love ive been trying to complete since Live.
I have been stacking every possible, available +regen boost from IO sets, regen at the cost of all things.
The tank I did this with in Live was pretty obnoxious in the arena, very hard to kill, long fights.
I think I want to do something similar with a sentinel.
If I were going to do this with full passive regeneration in mind I'd go Willpower again, my attack would have to be rad, being able to 2 slot analyze weakness for 10% regen in every attack is nice.
But if I were to ease off a little and just pick the best attack power for PvP, I'm not sure which way I'd go. I like the idea of Dark because, as a total passive regen build, making my enemies miss gives me more ticks between hits.
So it's really between rad and dark.
Make me harder to hit or make them easier to hit, tough call.