I feel you have to break down what you want from a "club". If you want discounts then of course GS/CW will provide you with not only the store discounts but campground discounts as well. If you are looking for campground discounts your club of choice may be pass port america or coast to coast.
However if you are looking to join a "chapter" within a club Good Sam would be the one to join. You would find a chapter nearest your home and make contact. The rest would be up to you and the chapter folks.