Day trip to Siena from Florence take train or bus?

I've used the bus multiple times and it's a great option. The walk from the Piazza Gramsci bus station to the Campo is relatively level and takes about 10 minutes. Much of the bus route is on a freeway. I'm not sure whether the train takes a more scenic route.

I took the bus also and what I remember most was the narrow Italian roads and how superbly the bus driver negotiated!

Bus is faster and once you get to Siena it drops you right outside the entrance to the old city center whereas the train station is either a very long boring walk or a taxi ride away.

I've done both - and would recommend the bus for the reasons others have stated. The train ride isn't bad, but it nearly always involves a change at Empoli. Last time I made the journey, the train was also slightly more expensive. Scenary wise, there is not much to see either way. The train takes you past an impressive castle near Poggibonsi, the bus passes close to Monteriggioni.

If you do arrive in Siena by train, there is a stop to the left and across the road from the station entrance from where you can get the bus up to the city. If you prefer to go on foot, there are several escalators starting in the shopping complex directly opposite the station entrance that will take you up to the top of the hill level, but it is still a fair walk to the city centre.

We also took the bus from Florence and it took only 1 hour. TIP: if you take a double decker, sit on the lower level. the upper level rocks more and my daughter got car sick. Have fun.