If you have 3 nights, pick a place and spend them all there. If you're more city travelers, pick Florence, if not, any town that appeals to you based on what you want to spend your time doing. Personally, I'd spend my 3 nights in Florence - spend the first day wandering around a bit and looking at the buildings then spend the evening at a wine bar, second day do a food tour, third day hire a driver to take you out of the city for a winery or two, last day whatever else you want to do before leaving town. Staying in one place will maximize your activity time by not eliminating most of a day in transit - packing up, renting a car, checking in, unpacking, returning the car all adds up, even if you're just going an hour away.