225-250 is best, and I prefer 225. Over 275 you aren't really smoking at that point, just grilling. Over 275 the wood is just straight burning instead of smouldering, you risk drying the meat out, and you are more likely to overcook the outside by the tikr your internal temp comes up. The lower the temperature the more smoke your hardwood will put out. Also generally speaking the lower temperature you cook at the more tender the meat will be.
Best way I have found to smoke a pork shoulder Is to trim the fat cap to 1/4" or leave it intact (fat will come off easily when you carve/pull, but all that fat will mean you are tossing a section that was rubbed and you'll have less bark). Rub the shoulder with garlic flavored olive oil (commonly available at grocery) instead of mustard, pat your dry rub (enough that its not falling off when you pick the meat up) and wrap in plastic wrap overnight. If you can't do overnight, give it two hours. I don't find this step particularly important- Using a dry rub lends to a better bark, but if you buy quality meat and use the right would park will have an absolutely delicious flavor without any seasoning at all. I don't find how long you let the rub sit to be very important because after 2 hours you are talking about penetrating the meat fractions of an inch, no matter how much rub you use or how long you let it sit it isn't going to flavor the inside of the shoulder. What's more important is to mix the pulled pork before serving so that every plate has a mix of the tender inside meat (won't be affected in flavor by the rub) and the outer bark with smoke ring (entirely flavored by tub and type of wood). Remove the pork from the fridge and let it start coming up to room temperature right before you prep your smoker or grill. Make a mop sauce using half apple juice, 1/4 red cider vinegar, 1/4 cooking oil, and some of your dry rub.
The next step gives you two options:
1) Smoke at 225, mopping or spritzing about once an hour until you hit internal temperature around 170. Then double wrap the shoulder in foil, pour about a cup of your mop sauce in the foil, cook until internal temp of 195 or so, then pull the foil and leave it on about another hour so that the bark will firm up. This method is much faster because it overcomes the stall, and it near guarantees tender and juicy pork. Downside to this method is that your bark will not turn out particularly great.
2) Smoke at 225 until you reach desired internal temperature (I would go 190-195), mopping or spritzing every 45 minutes to 60 minutes. This is the simpler old fashioned method. It produces the best bark, it could take up to 4 hours (or more) longer than wrapping with foil, you risk letting the meat dry out, and near constant supervision is required. That being said, the bark is so much better that if I have the time (14+ hours) and I'm not on a deadline like when company comes over and you want to eat at a specific time, I go this route.
Good luck, have fun.