Best way to get to Siena from Florence

The usual suggestion is to take the bus. The bus station is closer to the historic center. I don't suppose it makes much difference for a multi-day stay if you're not pressed for time. You could always hop on a bus from the train station or grab a taxi.

I'd take the Bus 131 from Florence to Siena. There are 3 to 4 buses going to Siena every hour. The last one leaves at 20:15.
https://www.tiemmespa.it/lineetpl/131.pdf

It bus station is near the main train station. The exact address in Florence to it is:
Via Santa Caterina da Siena, 15/17, 50123 Firenze FI,

Search that in Google maps

We took the bus from Florence to Siena, as well. We also took the bus (this one was FLIX) from Siena to Rome.

Thanks everyone! Is it worth buying the bus tickets in advance or should we just buy them at the station?

I really appreciate it! This forum is a life saver!

I would buy it at the station.

I wound up taking the train. Certainly, you can take a taxi up into town, but there are also a series of escalators you can use (7 or 8 flights, the first 2 through a shopping mall). Both times, there was one flight of escalators that wasn’t running, and it was a few blocks walk to where I stayed. Fortunately, I had packed light. The bus would have been more convenient, but the train was certainly doable.

You can just buy them at the station. It may not be as busy in Florence, now, but when we were there, we were glad we had allocated extra time, the bus ticket lines were a bit long

We've always taken the train ... about an hour and 20 minutes from SMN.
A taxi from the Siena train station to the front door of your accommodation costs about 12 Euro.

We've used the Siena escalators several times and once we thought one wasn't working because it wasn't moving, but it turned out that all we had to do was walk up to it and it started up again. Some kind of motion detector thing, I guess.

Cdtravel - We have frequently traveled between Siena and Florence. We always take the bus - be sure to take the "Rapido" which does not stop until the very outskirts of Siena. It takes 1 hour 15 minutes and arrives right on the edge of the City Center at the main Siena bus station. We will be in Siena for the next 6 weeks, perhaps we can meet for coffee!

Hello,
Bus or train. Public transport is great and very easy to use all over Italy. You can buy bus tickets same day- trains you may be able to save $$$ buying in advance.

The trains from Florence to Siena are all Regionale, so there’s no point trying to buy in advance - that only applies to the high speed trains (Florence to Rome, for example).