Try to avoid a rental car in Italy! Our driving style is very different than here in the US. Our roads are narrower, and we have a lot of traffic, even on highways.
Art cities have limitation to car circulation and the traffic can be a nightmare, especially in Rome, Naples and Florence; cars are simply banned in Venice. If you think that in the US gasoline is expensive at $3.00 a gallon, think again. In Europe, and Italy is no exception, gasoline runs over $8.00 a gallon (gasoline is sold by the liter and paid in Euro, I just converted these values for you). Now the cherry on top of the cake; finding a car with an automatic shift is not easy. As I said we have a lot of traffic and Italian drivers run pretty fast; you need to be very focused on driving; why should you miss the beauties of Italy just because you have to drive? Use public transportation instead! It is not expensive, we have an extended network of transportation means and you can relax. Even the famous never on time trains, are much better than here in the US; I used occasionally trains in America and I rather walk than use them. A ride from Rome to Florence (a bit less than 200 miles) is 90-100 minutes, and as today the cost is 36.00 Euro (per person, in coach; don’t use the first class), or about $54.00. Not really cheap anymore, but you can experience the thrill of traveling at 150 MpH. You can even make reservations from the US; just follow this link.