Website to book train from Florence to Rom

Valerie,

You can book your train tickets at Trenitalia.com.
You'll need the train stations in Italian; namely; Firenze S. M. Novella and Roma Termini.

The freccia trains are high speed trains that will get you from Firenze to Roma in about 1.5 hours.

Enjoy your trip!

Good info here that helped me book Firenze SMN to Roma Termini tickets.

Additionally, take a look at Italo:

http://www.italotreno.it/en

This is a private rail company serving Italy's major cities, and they usually offer competitive, if not better, rates.
In either case, the two stations you're mostly like going enter in the search boxes are Firenze S.M. Novella (Firenze SMN on Italo) and Roma Termini.

Thanks so much!

Valerie,

If you can commit to a specific train departure, you can buy tickets in advance either on the rail company websites or at www.trainline.eu at the same prices (Trainline sells tickets for both rail networks). You'll be using a high speed train on that route, and you'll have compulsory seat reservations.

....Can you tell me the best train to get there?.... There is no best train. Almost all the same except for speed. Pick a train that best fits your schedule. Second class is equal roughly to business class on the airlines as to seat size and space. First class will give you wide seats but little gain in leg room. All the trains are pretty comfortable when compared to an airplane.