Starting Italy trip in Orvieto staying 5 nights in bed &breakfast in Orvieto touring Umbria and southern Tuscany with car. Spending 6 nights before returning to Rome. Would like to visit Florence for a day and if possible Cinque terre. Should I base myself in Siena or Volterra
Anywhere in a small town or agriturismo (farmhouse) in the vicinity of Colle Val d’Elsa (or even Colle VE itself), as close as possible to an entrance to the Siena-Florence freeway. You can peruse Google Maps to see some and then search further on their websites.
From Colle Val D’Elsa everything important will be less than 30-45 minutes away (Siena, Monteriggioni, Chianti, Florence, Volterra, San Gimignano, Certaldo, etc.).
The Cinque Terre is not near anything however. To reach Riomaggiore by car you will need at the very least 2.5 hrs, so not an ideal day trip.