I bought every one that was available when I hit the road full time. Didn't or couldn't use them.
It really depends on HOW you full time. Traveling around most don't work because they have SO MANY restrictions, I.E. Which day, what time, what month, what year, what color the sky is on that day to get a free day or reduced rate.!!
So if you are one of those that plan your life a month in advance maybe you might luck out on using the memberships that have all the restrictions. Just didn't work for 'my' style of RV'ing.
As far as GS goes in the last few years I kept running into CG's with the GS logo that didn't offer the discount anymore OR they claimed it was 'already' in the posted CG rate. :R
The only one I DO use is KOA. It is what it is and if the the CG is a KOA you get the discount. And I just love their simple catalog with all their CG's across the USA. Great maps/directions, and phone numbers that actually work. Which after a few years full timing traveling I seek out and stay at KOA's when they are available in the area.