Florence was much cleaner(a far cry from all the cigarette butts covering Rome), calmer because of less crowds, and has such beautiful layers of history. It was once the center of medieval Europe and is the birthplace of the Renaissance. Visiting the Uffizi gallery can be just as overwhelming as the Louvre in Paris, though much smaller. Just for a list of the great works there http://en.wikipedia.org/wiki/Uffizi_Gallery
My second time here; definitely a favorite place.