Can you tell me more about what you are looking for? Smaller places with more intimate meetings, or bigger places with more of a tour or walk-in type of vibe?
The best visit + winery combinations I’ve had in Montalcino were Uccelliera, Lisini and Fuligni, in that order. Superb producers, on great rocky sites closer to town. But nothing flashy or fancy at all.
Poggio Antico was quite different. A very large, sleek, modern, Napa-ish tasting room. On lesser terroir, I think, getting into the gently rolling hills farther from town, but they make very pretty wines in a more modernish style but not excessively so. It was nice, but like I said, nice in a Napa type way. The restaurant was closed the day were there, but they referred us to Bocon Divino just outside of Montalcino, which was excellent, had a spectacular view from the patio, and served all the Poggio Antico wines (including the Riserva) by the glass at very reasonable prices. (The restaurants around Montalcino are superb, particularly the more rustic ones.)
Banfi really doesn’t do it for me, and I’m not one of those snobby Europhile types, but the place seems very Disneyland, the restaurant, while fancy and splashy, wasn’t as good as the better modestly priced ones in the area, I thought. I also think the wines are fine but not especially good, and you’ll see why if you go there – their vineyards are on the expanses of flat farmland on the periphery of the too-large DOCG, really nothing like the rocky, dry vineyard land closer to town. The lesser terroir and grapes are compensated to some degree by more oak and so forth, but they really lack the purity and focus of the wines from good terroir.
Ciacci Piccolomini is a good winery, in the good terroir (located fairly near Lisini and Uccelliera, I think). The visit was more impersonal, but fine.
Casanova de Neri is a controversial producer. They do have vineyards in great terroir, but their upper tier wines are pretty heavily oaked. They are much better than the large commercial producers in the flatlands like Banfi and Frescobaldi, but they are big and modern (except for the regular/base Brunello, which has less modern treatment) and need many years to integrate. You can do a short tasting-only visit there, or book a tour. I just did the tasting, and it was nice, plus something you could do as a short third tasting on a day.
I think you should book one in the morning, one in the afternoon, and that’s really what you can expect for the day, especially if you’re driving over from Montepulciano. Driving around that area is lovely, but much slower than it appears on a map.
A good plan for a day would be to pick two of the good producers near the city of Montalcino like Uccelliera, Lisini or Fuligni (or whatever other ones you learn about – I’m sure there are many other good ones), book one in the morning and one in the afternoon, eat lunch at one of the great restaurants in and around town, and maybe if you want to push it, either taste more in the Fortezza in Montalcino or make a shorter visit to somewhere like Casanova de Neri or Ciacci Piccolomini. That will make for an awesome and pretty full day.
Have a great trip.