Siena or Florence in May

How do you plan to move around?

Train or bus primarily, but we're not opposed to renting a car for a day.

It depends on whether you have been to Florence before and whether you want to see it or not. Both cities are suitable for day trips with bus or train to Tuscan towns (although Siena has limited train service), it depends on which towns you want to visit. Some are more easily reached from Florence, others are more easily reached from Siena.

If you want to stay in another smaller location, then you should rent a car.

This a good guide to what you can see in Tuscany by train or train+bus.
https://www.wanderingitaly.com/maps/images/tuscany-rail-map.png

Siena is a big city by rural Tuscany standards but does give a good feel for what hill towns are like with old buildings, sites and tons of history. Siena deserves at least a day all by itself and is a good place to arrange for a tour of some nearby towns and/or wineries and get a glimpse of the rural Tuscan lifestyle.

Florence has an embarrassment of art, history and culture and deserves at least a couple of days to itself. Check the list of sites in Florence and see what might be on your must see list - David and Uffizi are big for many people - and see how much time you want to spend there.

I would suggest at least a couple of nights in Florence, then Siena with a potential day trip to one more rural towns with the amount of wine or food tasting that you're interested in.

Keep in mind that most people here count nights rather than days since it's clearer and helps you know where to book lodging but keep in mind that two nights somewhere is only one full day sandwiched between days of packing, checking out, traveling and then checking in. Stating how many nights you have makes it clearer for people when they suggest itineraries and how much time to spend in places.

Have a great trip,
=Tod

Thanks Tod, good suggestions. I clarified my post, we're planning 5 nights.

You can use the website below to determine what you want to visit.
https://www.borghiditoscana.net/en/

Florence needs at least 2 full days to see just the very basics. Siena is another day affair. Some people visit Siena from Florence on a day trip.

Besides Siena itself, Lucca, Pisa, Pistoia, Arezzo, Cortona, Northern Chianti, maybe Volterra (via Pontedera) are more easily reached from Florence.

Val d'Orcia (Montepulciano, Pienza, Montalcino, Buonconvento) is more easily reached from Siena.
Alta Val d'Elsa (Monteriggioni, San Gimignano, Colle Val d'Elsa) and Southern Chianti are between the two, but slightly closer to Siena.

If you've visited Florence before, I'd probably stay in Siena, unless you are interested in the towns that are more easily reached from Florence.
If you have never been to Florence before, then I'd probably opt to stay in Florence.
With only 5 nights I wouldn't split my stay, since the transfer from hotel to hotel takes time, and I'd rather use that time for an extra day trip.

I think I'd rather base in Florence for 5 nights. We stayed there for 6 nights as first timers in March 2023 and thought that we'd plan day trips but we found more than enough to do right there. It's a compact city so you can walk everywhere and really wander at your leisure so you can make it a more relaxed pace rather than hustle and bustle. There are a lot of options for day trips including doing a day tour of some of the hill towns and famous wine areas, these might be worth the splurge if you want to save the hassle or renting and driving yourself. Or you can use the many public transportation options to go in a few directions (Lucca, Pisa, Sienna etc).
I visited Sienna as a day trip, driving from our agriturismo in March 2025 and really enjoyed seeing the town but I'm not sure I'd want to base there because of limited train access.

We want to enjoy a leisurely time rather than hustle and bustle.

I don't think you will avoid hustle and bustle in either Florence or Siena. Both very crowded and touristy.
Sounds like you are looking for a hill town experience in the countryside and for that you would need a car.

Florence needs at least 2 days although that is woefully short if you are interested in art.