When cooking meats such as pork chops in a toaster oven, is it better to use butter or some type of oil to coat the pan?
Also depends on how hot your toaster oven gets. Butter burns at 350 F, most oils dont burn until at least 400 F.

Heres a list of temperatures at which different oils burn http://whatscookingamerica.net/Information/CookingOilTypes.htm

Usually Ill start with oil and add some butter towards the end for flavor if Im cooking on a high heat.