*Any size works, just use all one size so they cook evenly, and the bigger the size the longer they will take to cook. Here is a generally guide:
Small (cherry, grape, etc) – 2-3hrs at 250˚F
Medium (plum, etc) – 3-4hrs at 250˚F
Large (beefsteak, porterhouse, etc) – 4-6hrs at 250˚F