How can anyone answer this?
What are you interested in seeing / doing?
If, as a "solo traveller", what you are looking for is "things to do", forget Bergerac, Limoges or Dinard. And, if you are looking for "things to do", it's difficult to advice you without knowing your tastes. Sport ? Culture, history ?
A town as la Rochelle, that is to say an important normal lively town and a tourist town has nothing to see with Dinard, , or even Carcasonne, for exemple, in term of possibilities for a solo traveller. Bergerac is, in french, very "provinciale" , so a little boring out of season, and not very tourist.
You'll be able to do a lot of wandering around! If you're only coming for a couple of days you'll be able to take a day trip on the train to either Sarlat or st emilion for a change of scenery too.
As Bernard says - what are your tastes...food & wine, chateaux, caves, history, canoeing...?? Hard to give suggestions when we don't know you! Also, will you have a car? If so, you can easily get to chateaux, wineries, river canoeing spots. If not, I think it will be limited for you.
Not knowing your interests, who can tell what would appeal most. Carcassonne is the biggest "name" in terms of attracting tourists
Limoges has a couple of museums we found very interesting, the municipal (art)museum and the Museum of the Resistance, and the medieval cathedral is beautiful, but maybe none of that appeals to you.