Not only have I been many times with the family, I have also been a holiday rep... as have my brother, sister, and best friend!
I worked for Havan Europe, brother and best mate worked for Keycamp, and Sister worked for Canvas.
I would say you get much the same service and standard of accomodation from all three (and the likes of Eurocamp) so your best bet is to compare prices. If you don't want to book through a company just get one of their brochure google the sites - a lot of them you can book direct as well.
I repped in the Vendee btw - and I wouldn't particularly recommend it as I think there are much nicer areas to go to.