There are many possibilities all around depending on what you are looking for. Will you be interested in visiting châteaux ? Other towns and villages in the Loire Valley ? Gardens ? Troglodytes dwellings ? Arts oriented activities ? Markets ? Canoeing or kayaking on a river ? Wines tasting ?
If you are driving the problem could be parking in Tours itself and getting around the maze of one way systems.
It will depend of which castle you want to visit. For Tours versus Angers, Tours is nearer some blockbusters castles (Chambord, Chenonceaux), but Angers give the possibility to spend a day at sea side. 1H15 from St Nazaire, or Pornic/ Le Croisic by car or train or car. Driving in Angers is also easier. For castles or other visits, including Saumur area, there are many possibilities : Serrant, le Plessis Bourré, le PLessis Macé, Brissac, Montreuil Bellay, Saumur, Brézé, Fontevraud. For bicycles Angers has also more choice of cycling pathes, and there is a beach in "lac de Maine", at 3 kms of the center. If you are interested by plants, you could visit terra botanica.
Thanks for the replies. We're staying in an apartment on the outskirts of Tours in the 2 lions area so will be getting the team into the city. We're certainly interested in visiting castles, but would also be interested in canoeing etc.