Car or train

A car can be a burden in cities, especially in Venice, Florence and Rome.
Italian trains are a great way to travel from city to city.
You don't really need to buy train tickets far in advance but if your plans are firm, you could benefit from deeply discounted fares.

the two train companies to look at fares and schedules are
Trenitalia and Italo.

I am planning our July trip and after much research have decide to mainly do trains. We are spending a few days in Tuscany (may or may not stop in Florence as we have been before) and will be renting a car for those days and then back to trains for us.
You can pre-purchase tickets on https://www.italiarail.com starting 120 days prior to your travel dates

Enjoy your trip!

I have often rented cars in Italy. Last fall, however, I used the train exclusively. I started in Rome and then went Assisi, Parma, Ravenna, Vicenza, Padova and Verona. I found traveling by rail to be stress free, comfortable, convenient and very economical. I purchased non-refundable 2nd class tickets on the Trenitalia web site a few months ahead of time. I highly recommend the Italian rail system.

I recommend the train. I have made that trek twice in the last 4 years. I prepurchased train tickets through Trenitalia. It was very easy and the trips are relatively short on the high speed trains. The trip for Venice to Florence is roughly 2 1/2 hours and Florence to Rome is 90 minutes. You can save a lot of money buying super economy tickets, but you are locked into a specific train. If you decide on the train, make sure you create an account on Trenitalia so you can go back and retrieve your tickets. I have never had an issue, but others on his forum have posted that they did not receive the confirmation email and PNR. Without an account, you would have to call them and hope you can get the PNR. With a car, there is the hassle of picking up and dropping off as well as the ZTL problem in Florence. No need to risk getting a traffic ticket 6 months after you return home.

If you are travelling around either Easter Monday or the 25th of April, I wouldn't wait the last second to purchase train tickets.

A site like www.viamichelin.com will show you that there are the mountains between Bologna and Florence. Even if the new A1 motorway deviation (called "Direttissima" on signs) runs straight in tunnels under the Apennines, you'll have to slow down at 110 kms per hour. Both trenitalia's and italotreno's high speed trains run under the same mountains at 200: no contest.

Do you already know about ZTL zones where non residents' cars can't enter? There is a camera controlled ZTL in every Italian settlement these days, not only in Florence. If you're going to drive, in Rome look for rental agencies inside the Borghese underground parking: it's far from the ZTL. Unfortunately I have no similar advices for Florence, you'll have to google image the ZTL signs and remember them.

Lauri,

For the places you'll be visiting, travel by high speed train is absolutely the best method and the most efficient use of your holiday time. No car can match the 300 km/h speed of the trains, and the trip will be more enjoyable without the worries about ZTL areas, speeding tickets, tolls, high fuel costs, etc. The trip from Florence to Rome is only about 90 minutes.

It's also important to note that for driving in Italy, each driver listed on the rental form must have the compulsory International Driver's Permit, which is used in conjunction with your home D.L. (so you must carry both). These are valid for one year, and easily obtained at any CAA/AAA office (two Passport-sized photos required, which may be provided by the issuing office).

There are also some potentially expensive "caveats" to be aware of when using trains and other public transit in Italy. If you need more information on that, post another note.

Tickets for trains in Italy can be purchased at www.trenitalia.com, www.italotreno.it, www.italiarail.com or www.trainline.eu (I normally use the latter website as it also sells tickets for trains in Germany, France and other countries, and their website is very user friendly).

You don't want a car (Rome and Florence ) or can't use (Venice) in any of these cities. Use the train. If you are planning on going into rural Italy or Tuscany then a car is a benefit. Don't drive in Rome--it will shorten your life!
Enjoy

I concur that train is the way to go, and book ahead for best ticket prices. Trains are easy, comfortable, fun, and comparatively cheap in Italy. The train network is exceptionally good, too. After reading all of the posts on this board about tickets for ZTL and other violations, I think driving in Italy is a very bad idea generally. Even more so when you are going to major cities. I have driven extensively in eight or nine countries in Europe (included Portugal and Ireland which are statistically high risk for accidents), and not driving in Italy is one of the things I am most sure about when it comes to planning trips. There is no hill town that is so tempting that I would try it. For me, I would plan an itinerary to avoid having to drive--I feel that strongly about it. No insult intended to the travel acumen of anyone who differs on that point, but that's the way I see it!

I have traveled extensively in most of Europe and never rented a car. I like to use public transportation, trains and buses. I sit and look out the windows and enjoy the scenery.
I always pack very light, so it is not a problem for me to get to my hotels (drop off bag) and then head out for sightseeing. I've booked lots of local tours for things I wanted to see with a guide for additional info.
So, in answer to the question - Train.....

If visiting only those cities take the train only

I would take the train. You don't have to worry about getting lost or driving through a ZTL zone. You just board and watch the scenery pass by.

For more information on trains look at Train travel here and use http://www.seat61.com/

Train travel is great. You can buy your ticket ahead of time which is the most least costly way. It will normally have the train number, the train car number and a seat number. Inside each train station there is a large departure board with the Destination city, intermittent cities, train number, track number and departure time. The main thing is the train number and track number. If you buy your ticket state side and print it out, all you have to do is board the train. There are high speed trains between your cities. The train seats are like coach airplane seats. You can grab a sandwich at the station to eat on the train or you can visit the dining car if it has one. For us it has been our preferred means of travel.

Just be sure you notice the departure time and then walk to the track where the train is arriving ahead of time. A city like Venice St. Lucia is a departure station. TRAINS LEAVE ON TIME. If you have time, walk down the track until you find your car. If pushed for time, hop onto the train at the first car you come to and walk down the aisle until you find your carriage and seat. Always look at the signs before you board. Nowadays, the trains have electronic signs beside the doors so you can check your destination. About 5 or ten minutes before the stop you are exiting, get up, gather your things and move toward the exit. Some times, if you wait until you are in the station, you will not make it off the train. Most stops are around 2 or three minutes, 5 in large cities.