We booked Hotel San Ranieri for 1 night as we arrived in Pisa very late in the evening and did not want to spent to much time on the road after landing. Our primary criteria to select our hotel was therefore the location (airport proximity).
When we got there (after approx. 15 min drive), we were positively impressed by the hotel: it is rather smart and offers a great service, considering the price. Plenty of choice for breakfast (even I found something I fancied eating, that's saying something ;) Clean and comfortable room, larger than the average european hotel room. Restaurant menu was appetising and moderately priced, though we did not get a chance to give it a try. The next morning, we walked at a leisurely pace from the hotel to the centre of Pisa (about 40min), so not long at all if you go by car.
For stopovers in Pisa, I would definitely recommend Hotel San Ranieri. If you are looking for a room with a view, then this won't be it!