My wife and I just completed our stay in the Loire Valley and it was amazing. Rick Steves recommends staying in Amboise but we decided to rent a car and stay in the smaller town of Loches. Loches was an excellent home base and a wonderful little town. It has so much history and the people were great. Walking the narrow streets and not having to fight through any crowds made Loches an excellent home base. The restaurants and cafes were excellent.
Loches provides an excellent triangulation with the chateaus East and West of Tours so we were able to see chateaus on both sides. If you are considering the Loire Valley I would highly recommended Loches as your base and staying at Phillippe's "Vie de Chateau".