I would recommend the Loire valley, though I am a bit biased towards it for some lovely memories there. It's got some gorgeous, extremely well preserved castles with beautiful parks where you can wander and enjoy the beauty of both the architecture and the scenery, if the weather is nice. It's an area that's very rich in history. I've found places like Reims tend to be more run of the mill French towns - they have their cathedrals and museums, of course, but aren't quite as exciting.