How best to explore Lucca, Pisa---by train or auto?

For 1st time Italy drivers, I would advise against doing Lucca and Pisa by car - both cities are full of one-way streets, have ZTL zones, and parking is not so easy, especially considering baggage in the boot. You should also consider just visiting Lucca as there's plenty to do and see to occupy a day.

Driving to Lucca is not problem, just understand that driving INTO the walls of the old town, you'll be severely limlmited because of the ZTL restricted driving zones. Find out from where ever you're staying where to park your rental and leave it there. When I remember visiting rush-hour outside the walls was rather crazy, took forever to travel thru the newer part of town. Lucca's train station isn't that far away from the walled parts of town, with luggage depending on where your accommodations are, it could be a challenge. Check distances and hit up the taxi stand if needed.

Pisa, I gotta admit, not one of my favorites and very highly ranked as most over-rated site. I'd opt to skip it and continue on to San Gimignano, however if you're locked-in and interested, don't let my opinion deter your interest. This is your vacation.

Welcome to the forum!

Trying to fit Lucca, Pisa and SG plus a rental car pick up all in one day then get to Siena is far too much- it simple will not fit. '
Lucca deserves a few hours. Pisa needs a few hours.
Same for SG.
If all of these location are must dos-

Here is what I would suggest:
Take one night from Siena
Take early train to Lucca for the day- drop your luggage at station- leave Lucca about 3-4 pm- train to Pisa.
See Pisa in the evening- we finally got there a few years ago and honestly I was impressed. The Field of Miracles all lit up at night is a gorgeous sight to see. I am not sure how late the buildings are open but try to at least see the Duomo and Baptistery this evening.
We stayed at a hotel right next to the Tower- Grand Duomo Hotel- it was inexpensive with a very good bkft.
grandhotelduomo.it
Our room had a view of the tower, felt like you could reach out and touch it we were that close

Once you have seen what you need to see in Pisa (don’t miss the Camposanto) take a taxi to the airport and pick up your car there. (The reason I did not suggest Lucca is because the availability at smaller rental locations like that is always limited, usually no automatics, etc).

Drive to SG- see that town- Only needs a few short hours- then on to your hotel in Siena- 2 nights.

I don’t care for one night stays but in a plan like this it is often a good choice.

I would only add that we collected our rental car from the Pisa train station a few years ago and it was pretty seamless. The location of the rental car lot is right next to the Autostrada heading east - made it a snap for us to drive to Siena that day along the SR222 (Chiantigiana) road.

Visit both Pisa and Lucca on the same day from Florence by train. Devote the first half of the day to Lucca, then from Lucca take the train to Pisa San Rossore station, 10 min walk to Piazza dei Miracoli (Piazza Duomo), where all sights are, and finally make your way to Pisa Centrale dor your return to Florence. You will need just 2 to 3 hours to see Piazza dei Miracoli in Pisa. There are about 3 to 6 trains per hour going from Pisa to Florence (and viceversa). The last train to Florence departs from Pisa Centrale one minute before midnight.

Forget renting a car to visit a Pisa and Lucca. Once you factor in the time for the paperwork to rent the car, find your way out of Florence, find parking, etc. it will take you twice as long as the train.

I would not trouble myself with trying to do this day by rental and car and I would definitely not try to cram in San G as well. Visit Lucca by train and if Pisa is still a draw on the same day then travel there by train as well. Travel to San G from Siena by bus.