Well, Willpower will boost your damage and Endurance your survivability. So if you want DPS, go willpower and if you want to focus on tanking, go endurance, right? I will admit I've been wondering the same thing as of lately. I'm going up the darkness tree as an assassin and most of my gear is focused on Willpower, and I've been thinking I should focus more on Endurance. But then again, the willpower-focused gear has been working well so far. Would like to hear other opinions here as well.