I've never done organized tour, but have ridden in both Loire Valley and Provence. Both are fantastic in a different way. It all depends what you're into. The architecture is different, climate is different, food and wine wonderful in both areas but also different. If you plan going in the summer, Provence will be hot, too hot for me but you might be used to it being from Australia. Loire is pretty flat, Provence hilly to very hilly.
The route along Loire is beautiful, it takes you on road and also on car free trail. Here's the info, you can also buy a set of maps at one of the tourist offices along the way.
http://www.cycling-loire.com/
In Provence we rode on road, didn't find any trails although there may be some. Make sure to take D roads, although some of them are quite busy as well.
Provence has a special place in my heart, so that would probably be my first choice, but Loire is also very beautiful. Languedoc is also very nice.
Riding in France is easy and drivers respectful. Anywhere you go, I'm sure you will love it. Of course it's up to you, but I don't think you need a guide. Just read up about the area to decide where you want to go, get yourself a map and you're set.