What are you looking to do? canoe, boat, tube, fish, party, etc. Any preference on how "rough" it is? Do you prefer car camping with quick access to hot dogs or looking for more survivalist trip.
I agree with Musky that some of the best are the smaller grounds but the bigger ones generally have nicer facilities (showers,etc). I also dont like to share the ground with RV's but thats just me.
I've been wanting to stay on Rock Island (Door County) for the novelty but with 2 ferries needed with the 2nd being a non-vehicle (carry in equip) its been hard convincing wife/friends to do and I'm not yet to the point where camping alone sounds fun.... Sites are nice though. You could always camp on Washington Island and do a day trip to Rock. Not too far from MKE.