In Michigan my favorites are:
Zingermans Deli in Ann Arbor, Mom went to Michigan and we had season football tickets, pretty much grew up with their sandwiches before games on saturdays. Amazing array bread, cheese and meat to choose from, some very "out there".
Another is Captain Nemos Subs, there are a few out there but the one I like is in Belleville, mi. That was my dad's hometown and my mom and dad went there when they were kids, its a hole in the wall pretty much but has just amazing food.