Why not be really rash and try both for a year? If after that you find you have a preference, or really don't see the point of either, no one will force you to renew your subscription. We have stuck with the CCC, partly because for several years we used a trailer tent, which would not have been allowed on a CC site, but also because I always ended up very depressed and anxious after reading the CC club magazine! There always seemed to be a new problem to loose sleep over!
In terms of what you will get out of membership, I have to say, I don't think there is much in it - both offer good (if somewhat over regimented) club sites, advice, a magazine, overseas travel, insurance, certificated site network etc, etc. I think it is really a question of finding where you personally feel most comfortable.