Nice property, with a lot of charm and historic character. Definitely spring for the garden view and note that although you might have a better view on the higher levels, we enjoyed our stay in Room 105 which was lovely and spacious-- it had an adjacent upstairs loft area with 2 single beds which would be great for a family with young kids. An added bonus was that it was only one level of stairs to get to street level. (The small elevator was a bit slow.) We were pleasantly surprised that the Palazzo also offered inexpensive wine for sale (from a barrel on the countertop) by the glass and carafe-- it was nice to be able to sip some wine in the garden and watch the beautiful sunset from the terrace. All the staff we encountered were friendly and courteous.
Free parking was a nice feature. Be sure that when you set your GPS, you take the route by the Porta San Marco gate. (Siena is closed to traffic in sections- not all city gates will get you to the Palazzo.) Breakfast was good (loved the croissants and their multi-grain, seeded bread-yum!) Would definitely stay there again.