In your area:
You already mentioned La Rochelle, so I'd have to suggest Concarneau. Beautiful little fort/town only a day's sail West from Morbihan. Tie up to the wall and clean your bottom at low tide with the other boats that will be there doing the same thing. Walk into that beautiful walled town and have a croissant and a nice meal.
We also enjoyed exploring the caves while anchored in Crozon, and the architecture and historic cottages/houses were fantastic. That's about a day's sail from Concarneau.
Europe is full of incredible places to visit. Ribadesella and Baiona are our two favourite (small) northern
Spain anchorages. Ribadesella's entrance is so protected, you can't even see it from sea. And Baiona's town and fort are full of
history, it was a major port of departure for the Americas 300 years ago. Both
anchorages are well protected, esp Ribadesella. (43,27N 05,03W)
Ok, we don't have a favourite, but you should see those four if you have the time.
Cheers.
Paul.