I have been a member of both in the past but have never stayed on a CCC site, I only used the membership at that time because their breakdown is tied into the RAc and having a company vehicle with RAC, they allowed me to just tag on Euro cover.
In many case too, not all CAMC and CCC sites tend to be very close together, or at least in the same locality and they dont offer an awful lot in variety of location. We use only CAMC sites low season but find in summer we can get better deals on commercial sites just prior to the main holidays.
CAMC sites do offer a decent standard of facilities across the network though some commercial sites are better, and some very much worse.
CAMC Insurance and Breakdown for us too nowadays.
One point I will add that is oft covered is the booking up every weekend in advance, and the sites being pretty empty midweek. Unless you plan in advance these days it can sometimes be difficult to get away at short notice, especially on popular sites.