Boston

Lobster, lobster bisque, clam chowder, the North End Italian cuisine from vitello to cannoli, The Museum of Fine Arts, The Isabella Stewart Gardner Museum, lighthouses, boat rides, it's a walking city with a good public transportation, the Charles, the Freedom Trail, Faneuil Hall, Cambridge, daytrips via commuter rail to coastal historic towns like Gloucester and Rockport, gorgeous foliage (lots of red maples), etc.

Because Boston is ideal in mid October, you might be too late to secure hotel accommodations so you might end up choosing Chicago by default.