Four of us are flying into Milan in October. We are staying in San Gimigniano and are weighing our options to drive or take the train from Milan. Any suggestions?
You will want to drive. I've driven to San Gimignano very conveniently. Training will likely be inconvenient when train changes are factored in and may involve a lot of walking with your luggage. Also a rental car gives you a lot of freedom in the area to explore towns that are unreachable by train.
Be sure to get a GPS for the car and make sure it's speaking English before you leave the lot. Signage in Italy leaves A LOT to be desired.
There is no train station in San Gimignano. The closest is Poggibonsi. From Poggibonsi, you take the frequent local bus to S.G.
To do this, you take the high-speed from Milan to Florence. At Florence, you transfer to a local train to Poggibonsi (about and hour ride). Then, you take the frequent local bus to S.G. You can also take frequent local buses to Volterra and Siena.
Having a car in Tuscany does have it's great advantages. Given that you can find parking, there are easy drives to Volterra, Siena and even Montepulciano. You can also visit the many wineries.