best gameplan for Italian cities

We will be traveling by public transportation--bus or train, whichever is either quickest or cheapest. We will be staying 4-5 nights in florence, 1-2 nights in Siena, and 1 night in San Gimignano.

You want to get to Venice by train, not bus. And SG does not have a train station in town; there's a train station in Poggibonsi but that involves connecting to a bus to get to SG. Therefore, two alternative ways to do what you want to do would be: #1: Take the train Rome - Florence, 1hr 35mins. Bus Florence - SG (no train station). Bus SG - Siena. Then train Siena - Venice. #2: Or , you could do train Rome - Sien, 3 and 1/2 hrs. (note: because the train ride is not fast, some do bus, instead of train, from Rome to Siena. Once in Siena, bus Siena - SG (no train station, except Poggibonsi). Bus SG - Florence. Then train Florence - Venice.

Skip Pisa, its not worth your time.

I think Kent's 2nd suggestion seems to make the most sense - less backtracking, more direct routes, which cuts on the stress. Another option is to not stay overnight in Siena or San Gimignano at all and just base in florence and do daytrips. that entirely depends on the kind of traveler you are. I agree Pisa is not worthwhile except for the area where the Tower, Duomo, etc. are. You could do a daytrip where you go from Florence to Pisa, take the bus to the tower and back (or do Rick's walking tour one way or the other), and be in Lucca well before lunch, before going back to Florence. that wouldn't be that stressful of a day I don't think.

Debra makes a good point, that going to Florence first, then SG, then Siena, then Siena - Venice, takes more time and involves a train change in Florence. Going to Siena first, then SG, then Florence, then Florence - Siena (my option 2 in my 1st post) would avoid the train change and extra time. However, cutting the other way is this consideration: Rome - Florence by train is only 1 and 1/2 hrs (on the fastest trains), whereas Rome - Siena by train is about 3 and 1/2 hours on the fastest trains, i.e., 2 hrs longer. Therefore, part of the calculus is, if you go Rome - Florence on that "first day", instead of Rome - Siena, the transportation time on that day is ~ 2 hrs less.

I would not sleep in SanG but would add an extra day to either Florence or Siena and side trip to SanG. We took a Chianti region tour while staying in Siena that also let us hang out in SanG. We were there for 3 hours and it was enough (for us anyhow) to see what we wanted to and walk the town.

Depending on what you want to see in Lucca, it might be too much to go there and to Pisa on the same day. As the others said, Pisa isn't that interesting. Go to Lucca in the morning and if you have the time and energy when you're done, stop in Pisa on the way back to Florence.