Which hilltop city?

I loved Montalcino, would have loved spending more days there.

Will you have a car? Buses can get you out of Montalcino for day trips.

We love Montalcino as well. There are many wonderful agriturismos around that area. Last time we were there we stayed here: http://www.canalicchiodisoprawinerelais.it/web/index.cfm?id=0E97327C-789D-4A5E-88F742FAB6074C5D&home

I would recommend a car for this area for sure.

We stayed in a B&B that we LOVED in Montepulciano and used it as a home base for exploring Tuscany. Seriously - we loved this place: http://www.lortodipanza.it/inglese/home_page.php. My kids still talk about it all the time.

We really enjoyed Montalcino, Siena, Volterra, and San Gigimignano.

We stayed in tiny Monticchiello (outside of Montepulciano) for 9 days a few years ago and it was the perfect place to use as a home base. It is less than 10 miles to Montepulciano and overlooks Pienza, but is a close drive or train ride to Assisi, Perugia, Siena and Florence, among other places.

There are not a lot of accommodations (we rented an apartment through VRBO) but in the evening it is peaceful and there are three world class restaurants (my review here... https://www.tripadvisor.com/ShowUserReviews-g787975-d2076421-r180871688-La_Taverna_di_Moranda-Monticchiello_Pienza_Tuscany.html#REVIEWS ) plus a lovely outdoor patio restaurant (la Guardiola) overlooking the gorgeous, quintessentially Tuscan Val d'Orcia.

I am finally returning to Italy in 2 1/2 weeks and no return would be the complete without staying at least one night in Monticchiello. I loved the place so much that I want it to be my home.

It really depends on the towns you want to visit.

South of Siena:
Montepulciano, Pienza, Monticchiello (in order of decreasing size) are all good. Montalcino may take a bit longer to get to/out of. I don't have a villa/agriturismo to suggest (others might), but you can search on any websites like agriturismo.it (.com, .net) or the majors like booking or expedia. One word of warning about those accommodations. They are sometimes in the boonies and may take longer than you think to drive to/from them from the main highways, therefore whatever you choose, plot it first on Google maps and calculate the time distances from there to the locations you want to visit.

North of Siena:
Alta Val D'Elsa area (Upper Elsa Valley): Monteriggioni/Colle V.E./San Gimignano/Barberino. Are all good and near the Florence-Siena freeway, therefore logistically great. Also easy for a visit to the Chianti hills.

We spent two weeks in an apartment in Montepulciano with parking and inside the walls; it was stunning. We had beautiful views out over the valley and the old historic center at our front door. This meant easy travel to surrounding areas during the day and then an easy stroll to one of a dozen or so restaurants in the evening. There isn't much basic shopping in the old city but there is a grocery store just outside the downhill exit to the town walls and we did locate the one tiny hidden bakery within the old town. The town itself is charming with fabulous views from the ramparts.

I much prefer being in a hill town to being near one as you can't drive and have wine with dinner and we don't much like driving on dark country roads at night anyway.

Thank you so very much.......These are all wonderful suggestions!
The choices of towns and or agriturismos and or B&Bs are just overwhelming! I've been to all of the usual sites.......Trip Advisor, Booking.com, Airbnb, VRBO, etc. and now I'm more confused than when I began my search. Hopefully, this will allow be to sift through options a little more clearly. Thanks again!

P.S.
I'm also open to B&Bs & Inns. Perhaps an incredible lodging recommendation will help in selecting a town?

Everyone has different preferences. For me the hilltop towns you are considering are very small towns not cities.
I would be bored out of my mind staying even a little outside of either of the towns at a villa or agriturismo for that long.

To me I saw no value in that, assuming you will have a car either way you can reach the countryside in minutes from town. If staying outside of town you cannot walk anywhere really except for your own property. I never saw pedestrians walking on the country roads where an agristristmo would be.

I would rank in order of preference:
1.) Montepulciano
2.) Pienza
3.) Montalcino

Stayed in Pienza this fall and love the area. Logistically Pienza is a little better because it is closer to the most scenic portions of the countryside and faster into and out of parking/car to town ; it is also in between the 2 others which is nice so neither other town is far.

If 2-3 nights I would probably rank Pienza first but with 5-6 nights, I would prefer Montepulciano. More charm, much larger and more to do.

There are other smaller towns in the area as well but they would be too small for me to stay that long in.
Also, keep in mind you are close enough to day trip to Orvieto, Siena, Florence, San Gim or Volterra and I am sure others from any of these locations in the Val D'Orcia.

We walked to La Grotte restaurant below Montepulciano's town walls at night and found even that quite frightening as rural roads are not designed for pedestrians. The ones outside the towns are pitch black as there is no street lighting. We felt at risk on these narrow roads even with some lighting. This is why we stay in small towns where we can walk to restaurants etc. Montepulciano (and presumably the other towns) have sidewalks and restaurants within the old town walls.

One of my favorite activities is going out for dinner and then walking home afterwards so count me in the stay in town crowd. With a car I might split time between two towns with two or three nights each. We are headed back to Montepulciano.