From near the southern border, up north is probably north of Mt. Pleasant. Cadillac for sure. My favorite place is the GH Day campground at SBD. Love that the beach is relatively secluded and not quiet and I can light a fire and take a bottle of wine to watch the sunset with my wife while the kids play in the lake. It's a local paradise.
Beaver Island and hiking on the Manatou's are phenomenal choices also.