Rent a car (or a driver)

The best way to travel Tuscany and/or Umbria is to rent a car. This assumes you have several days to devote to touring. There is no better way to see the towns and villages and countryside. AutoEurope ( http://www.autoeurope.com/ ) is a U.S.-based company that has always been the cheapest, easiest and most dependable rental company for me. You book your rental here, and pick it up from Europcar (or sometimes Avis or another agency). They don't try to take advantage of you (once, during a spot of confusion, we dropped off a car in Venice, on the sidewalk in front of a Europcar booking office having no place to park cars, rather than at the Venice airport, where it apparently should have been dropped. We pointed the car out to the Europcar duty person there, quickly handed him the key and our papers, and rushed off to where our wives were holding a boat to take us to our hotel. The fellow kept saying but, but, but... But they never billed my credit card anything additional for dropping at the wrong place).
Be sure to book your car or van before you leave the States...it's much cheaper than doing it after you get there.
I think Italian drivers are terrific (they go by eye contact with you regarding right of way and at intersections, I find), and it is always a pleasure for me to drive there. But don't try to drive in Rome, except to perhaps pick up your car at Fiumicino Airport to drive north.
And of course, always have a good road map with you.
If you are limited in the time you have to see the hilltowns and countryside, you may want to hire a driver/guide to take you on day trips. They can save you a ton of time. Once we hired a driver to take us to Siena for the day, from Florence. He whizzed us down there in his Mercedes, and delivered us to very steps of the incredible cathedral at Siena ( http://en.wikipedia.org/wiki/Duomo_di_Siena ). On our own, we would have had to come in the crowded tourist "front" way, parked, and walked for 30 or 40 minutes to get to the cathedral. But our driver took us in the back gate of Siena, which would have been nearly impossible for us to learn about and find. Plus, he parked where we would not have, and stayed with the car, in case it had to be moved. Most hotels will arrange a driver for you. And a driver will also provide local color and anecdotes you don't find in the guidebooks. They are well worth the money if you don't want to drive, or only want to do one or two day trips. Of course, there are group day trips to the most popular places. Your hotel or travel information office (look for the "i" sign on a building) can help you there too.