I guess I can add to this post based on the cities that I have lived in as a student.
Miami, FL - Attended the UMiami and did not have a car at the time. The public transportation in Miami is pretty poor. I managed to get around for the few years I was there, but not having a car really limited me in terms of what I could do on the weekends and the places I could go (the Metro line/buses do not go out to certain places). Fortunately, I lived right next door to a grocery store, so walked there and bought as much as I could carry. My commute to school from Kendall was like an hour one way.
Austin, TX - Went to UT and did have a car at the time. I lived so close to school that I walked every day. I think I probably only took the bus a couple of times in the two years I was there, but I hear that it is pretty good especially if you commute within the university and downtown areas. For going to the grocery store having a car is super convenient, although there was a bus terminal right outside of the store I used to frequent. For going out, taking a cab downtown is the easiest way to get there. There are always tons of cabs going and coming from downtown.
Madison, WI - A student at UW now and do have a car. The public transportation in Madison is amazing though. I take it to school just about every day. The way the city is laid out (on an isthmus) means that it is pretty compact and so the public transportation can take you virtually everywhere. For going out, there aren't as many cabs as there are in Austin just waiting for passengers and the buses don't run super late, which means that most people drive downtown. Overall though, Madison is probably the best place for public transportation among the place I have lived.