Either way you want to go man butt should turn out great. Foiling is more of a personal preference thing. Helps it through the stall and some say it does keep it moist. But if you are going for bark leave it unwrapped. I've done both with great results.
There is no "need" to foil (wrap) your meat with or without a water pan. It is largely a personal choice. You'll find folks from both camps here on the forum (I'm in the don't foil camp unless I'm in a hurry, which you should never be when you're Queing). Try both ways and see how YOU like it best.
I don’t foil butts much at all. Even with a “crusty bark” once you pull them the little bits of crust just turn into pockets of spicy goodness. The only disadvantage I see is that you lose a bunch of fat and juice that could be mixed back in with the pull had the butt been wrapped.