Where are you at in Michigan?
FWIW, Marquette South Trails are very nice. I've heard no end of good things about the Houghton/Hancock and Copper Harbor trail systems. Hansen Hills in Grayling has very nice trail system that I had a lot of fun on last summer. And there's Fort Custer near Battle Creek.
A good place to go for even better information might be mmba.org. Lot's of people from southern Michigan on that board.