For me it would be the River Charente between Angeac and Sireuil. The river is a chalk stream like the Hampshire Avon but navigable like the Thames. This gives breathtaking clarity in 12 foot of water with four locks, half a dozen at least weirs, mill pools and races with tremendous weed growth in places. The river splits and reforms many times so you can find tiny fast running streams, slow glides, islands, gravel bars and every other feature that you could wish for. Carp run to over 50lb, barbel to almost double figures and there are specimen pike, zander, perch roach and chub along with catfish of over 2,5 metres.
An added bonus is that with an annual Carte de Peche costing around €100 p.a. you can fish anywhere including from a boat with no extra charge. And, no close season for coarse fish. If you got fed up with that you'd be better off taking up golf.