What would you do?

Either will work, I'd go to Siena first and then come back to have more time in Florence--but then I love Firenze, I mean Florence.

Since we've never been, I wonder if we would want two days? Maybe go on the way, and go back again?

We just thought we might like a smaller town to stay in, and we are not necessarily into galleries.

Besides Galleries...what would you recommend? I think we would just enjoy people watching, but that could be done in Siena too.

I wasn't fond of the lodging in Florence but I think it would be hard to see the Accademia and Uffizi in 6 1/2 hours, let alone all the other sites. Even with reservations for the two biggies, I would think two days of touring with one night would be the minimum. Siena doesn't require three nights (but you may be planning day trips from there that you would forego to stay in Florence).

Florence is my favorite so I would arrange for as much time there as you can. Florence is very walkable. You can spend a lot of time just gazing at the architecture, walking along the Arno and the Ponte Vecchio, going to the outdoor markets, eating gelato, hiking(or riding the bus)to Piazzale Michelangelo for a view down onto the city, picking out a favorite statue at the Loggia dei Lanzi, throwing a coin and rubbing the boar's nose at Mercato Nuovo. I would also suggest seeing at least one church. A favorite is Santa Croce where Michelangelo and Galileo are entombed. I could go on and on. As for the Uffizi and Accademia, make sure you call ahead for reservations or you could spend precious time standing in line.

Your suggestion:"Since we've never been, I wonder if we would want two days? Maybe go on the way, and go back again?"sounds like a good idea. One day-trip really doesn't do justice to Florence, if you have more time than that.

Siena can be seen in a day, Florence cannot. I would stay 3 nights in Florence at the Hotel Casci on via Cavour and make a day trip to Siena.