Of those three listed-
SR can be made survivable with the fewest slots invested. Those slots, plus the 20% recharge can help offense. It lacks the layers of the other two, and the parry power is wasted most of the time once the build matures. A primary with AOE knockdown actually helps a lot more. Its hole is actually the level progression vs AOEs. Which is not there on Brutes.
Invul is the toughest, since you can softcap many typed defenses AND cap S/L resist, with other resists decent. DP heals and caps hp. The parry power can protect you when def debuffed or exemped. You do have that gaping Psi hole and attempting to patch that can eat a lot of slots.
Willpower is nice in that it has no holes. Its main weakness is slows, which hurt it offensively not defensively. It doesn't survive alphas as well as the other two, but has the advantage that adding defense and resist through IOs both makes you tougher and shores that problem up at the same time. You will get the most mileage of parry powers with WP. From personal experience once you get the typed defs around 30% you are roughly equal to a softcapped SR for most content.
The question of Kat damage was brought up. Its above average, but not one of the top performers. It is better than BS.