You can use the picnic or butt for pulled pork. The picnics usually have a layer of skin on that should be trimmed off and used for Chicharrónes. The picnic is actually a more tender cut IMHO and that is why many people prefer to slice it and not pull it.
But again either can be used for pulled pork.
I agree with Muebe!
Here's a pic of a whole shoulder I purchased and had cut in half. The picnic is on the left, the Butt is on the right.
For pulled pork I use butts & picnics both all the time, and when it's done, you cannot tell a difference. We just did two picnics for pulled pork for my daughter's graduation a couple weekends ago (because that's what I had in the freezer) and they turned out fabulous.
Many champion BBQ'ers use whole shoulders in competitions (Myron Mixon is one).
