I don't think you use either... butter and coconut oils are used for making edibles, once the weed is heated in the crockpot, you can't smoke it anymore.
Good advice. Coconut oil is for edibles ONLY. Never vape any cooking oil as it can result in Lipid Pneumonia. VG = Vegetable Glycerin PG = Propylene Glycol PEG = Polyethylene Glycol ONLY for making vape juice. Crock pots is fine if your making it for 500 friends otherwise you need more like a thimble. Metal bottle cap. My own expriments in making vape juice is here. Starts about page 200. An American Dream - White Picket Fences and Marijuana in the So Cal Sun. BNW