Originally Posted by
unbongwah
They're two separate things: PRR protects against physical atks; Evasion (+high Reflex saves) protects against magic/trap dmg. Ideally you have both, as well as high Dodge, concealment, and Incorporeality to round out your defenses.
I think the rule of thumb is you want Reflex saves at least twice your character level for Elite content; for Hard content I'd say that's closer to 1.5 * char lvl. That's just a rule of thumb, though; sometimes you can get by w/less, sometimes you need more.
AC is largely meaningless at higher lvls; certainly not as predictably useful as other defenses. Earth stance monk / kensei can get almost as much AC & PRR as conventional armored builds can; plus (Imp) Evasion, Shadow Form, and high Dodge, making for more well-rounded defenses. Add a pally splash for Divine Grace w/decent CHA and you've got a pretty survivable toon.