San Gimignano was my favorite! I went via bus, too, just 1 transfer, was pretty easy to get to, but a car will be much more convenient. I also visited Montalcino, Montepulciano, Pienza, and Volterra. Volterra was my second favorite, I rented a car for the day and drove out, it was an easy and gorgeous drive. It's fairly big for being a small hill town, so lots to explore, and they have a prison next to the old town that on some days it's possible to actually have dinner at, served by the (most well behaved and minimum security) prisoners, if that's something that interests you. Pienza, Montalcino, and Montepulciano are pretty similar, but all make for a beautiful drive through the Tuscan hillside. One of my friends on the trip exclaimed that the rolling hillsides looked just like Microsoft Windows' grassy background, so so picture perfect. Montepulciano is famous for where the scene in the Twilight movie in Italy was filmed, so those tourists love that. Otherwise the other two are a little cuter and offer better Tuscany views