Well in PvE Marauders are super-squishy. I outlevel mobs by 2-4 and still get withing an inch of dying and that's with my CD's.
In PvP, I do pretty well. But I hear good players always target the Marauders/Sentinels first, because healers can't outheal them.
Assassin did pretty well PvE, but I never PvP'd with him, so I can't help you there