Radda is more central
Ciao thecatmiami!
Cortona is a little further away from all of the main sights since it is further south.... Radda is definitely more central. It might look isolated on a map but it is smack in the center of the Chianti area so very central to all of the places you want to visit while here. From there it takes about an hour to get into Florence, 45 min to Siena.
It all depends on what you plan to visit while you are here - a visit to Florence and Siena are musts, then you can spend the rest of your time visiting Chianti, San Gimignano (Google maps say about 52 min). Radda will be perfect for this.
To get to most places you won't be taking any super highways -- that is why it takes time -- the roads are 2 lanes, go up and down small hills and the scenery is beautiful. So drives through Chianti will be a pleasure, they take time but are part of your vacation
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If you've been to Florence and Chianti before and want to stick to exploring southern Tuscany, then Cortona would be better positioned but I am assuming this is not the case....
