I highly recommend Carla's B & B. While most people probably choose her accommodations for a one night stay due to her closeness to the airport and the train station, I can say from experience that a longer stay is very enjoyable. It's an easy walk to the center of Bologna. Various buses are readily available, too. The residential neighborhood is quiet and tranquil with a variety of good restaurants and supermarkets. In my opinion 3 days to a week is the perfect stay.