Butt... should always use a butt roast.
The biggest problem I see with people cooking pork is they overcook the crap out of it and it becomes dry. Really tough cuts of beef require long cooking times, but pork generally cooks pretty fast.
I always coat mine with a good bit of dry rub, which varies depending on who you talk to. Most folks use brown sugar, garlic powder, onion powder, and paprika in varying amounts, but you can find a couple dozen rub recipes on the net. When you cook it, make sure you use an offset method, where all your charcoal is on the side opposite the vent and put the meat under the vent. That way the meat isn't exposed to direct heat but instead gets the heat rising up to get to the vent. Also, get a couple of wood chunks like Hickory, Apple, Cherry, etc., soak them in water for a few hours, and toss them on the charcoal before you put the grill lid down. That'll give you some smoke.
And the topper is you have to use a mustard/vinegar-based, AKA North Carolina, BBQ sauce. That's a must for pulled pork.
