5 Days To See Tuscany Hilltop Towns In September

A car is the most efficient way to see the hilltop towns of Tuscany.
Using public transportation is going to be challenging and take extra time.
This is one of the few times I'd encourage renting a car in Italy.

Leave Florence nights for last.
Rent a car upon arrival.
Find a country hotel or villa or farmhouse outside of the cities. There are hundreds all over Tuscany.
The best base is somewhere between Florence and Siena, preferably near the freeway connecting the two cities. The area just north of Siena (Alta Val d'Elsa, or upper Elsa valley) would be ideal (Colle Val D'Elsa, Monteriggioni area). From there you have virtually all of Tuscany within 90 min drive.
Do not stay in the city center of Florence or Siena with a car as there are strict traffic restrictions.
After your five nights day tripping around, drive to Florence and return the car upon arrival. Return the car at either the airport or, if you use Hertz, the Sansovino location. Do not drive inside Florence city center.
Stay in Florence without the car for your last 3 nights. On the day you depart use a taxi to the airport (less than 15 min from anywhere in the city center).

Glad to read your response, Roberto. We are booked in early October at a sort of agriturismo in Noce (a couple miles north of Barberino Val d'Elsa) with a rental car (picked up in Florence at Hertz Sansovino) and plan to drop the car back in Florence, where we will stay a few days before continuing on with our holiday. I'll be interested to hear how Jim's trip goes, since there are some similarities.

As mentioned above, visiting the Tuscan hill towns without a car is not ideal.
It is however possible. But it requires extra time since you need to deal with scheduled public transportation which is infrequent at some locations.
To do so I recommend to split your stay between Florence and Siena. Some towns are more easily visited from Siena, others are easier from Florence, which is Tuscany's capital and main transportation hub.
Since trains don't go on top of hills, often the best way to reach some towns is by bus.
Buses are particularly infrequent on weekends, particularly Sunday when there are very few runs. Therefore if you visit small towns by bus, do so Monday through Friday. Stay in Florence or Siena on weekends. If you travel on weekends go to places served by rail. Train service is just as frequent on weekends.

If you are limiting yourself to public transport I would get the train to Siena (3nts) from Florence.
Do a day excursion to San Gimignano, Volterra by bus from Siena.
Then train to Lucca (2nts) with a day excursion to Pisa.

I like being in cities in the evenings, so I would agree with staying in Firenze and Siena for a few nights each and daytrip from there. I love Montalcino, Pienza, Montepulciano, Arezzo, and Lucca.

Here's a related thread:
https://community.ricksteves.com/travel-forum/italy/best-most-picturesque-tuscan-hilltown-to-stay-at-for-3-4-days-plus-must-see-hilltowns-in-the-region