I also like a single speeds for commuting, as long as you don't have any massive hills in your way. The simplicty and ease of maintnance in poor conditions are real plusses. If the part of WI you are in is flat, a SS may be a good choice as a commuter.
I had a hybrid for a bit, but unless you are really wedded to a more upright riding position, get a road style bike. You will want to go faster soon... Used steel road bikes are great (often much nicer than the lower end modern road bikes you would get in the same price range).
Above all else, buy a good pump and learn how to fix a flat on the road. It is going to happen sooner than later.