These are from the same part of the pig but are not quite the same.  The butt is a meatier cut with more marbling. Marbling makes it a slightly more tender piece of meat. If you’re worried about the extra fat, don’t be. Much of it will cook off and only leave behind great flavor. While most people opt for a shoulder, rest assured both are flavorful and delicious. Boston Butts can sometimes be less readily available, depending on your grocery store.