I bought into all of them when I first started out. :(
I now do not belong to any. I am a full timer.
On some it depends on 'how' you RV. Just the weekends? Only on vacation? Snowbird, etc.
The ones that offer huge discounts come with huge restrictions. Certain days, certain time of the month, never on weekends and some the moon has to be in a certain phase before they will give you a discount. And never will any of the CG's around an attraction be part of these types of membership discounts. I found them to be worthless even with my time not be constricted as many RV'ers.
Join Good Sam and expect your mail box to be overflowing with junk mail, duplicate requests for renewal, and your email sold everywhere, etc., until you die. I had the us postal service shut down my mailbox while I was on the road because of the ridiculous amount of junk mail from them.
Escapees is mostly a full timer club. The discounts are at 'their' few CG's which I found them all to be remote locations and pretty much to be higher end resorts with higher rates to begin with.
I also found no real benefit with FMCA but a placard for the back of your MH with a number on it that anyone could look up all your personal info from.
Add up all the yearly costs of these memberships and see if it is worth the price to you based on your style of RV'ing.
BTW: All CG's have great discount programs for length of stay even it is not listed in their rates. All you have to do is ask them.
I usually can stay an entire month at any CG for around $250 to $300. If you were to pay by the day it with an average of $30.00 per day that would be $900.00. They also offer weekly and biweekly discounts also. Just ask the CG and you don't have to join no stinkn club to get the discount! :W