Joined them ALL when I started out.
Now the ONLY one I have is KOA.
With Passport America you REALLY have to read each CG 'website'. Maybe with long term way in advance planning you can glean a discount from them. But I never could in all my years full timing. Discounts were only on certain days the third Tuesday of the 8th month or when there was an eclipse of the sun, etc etc. The'exclusions' were endless. And most listed, when you went to call them they tell you Oh we stopped offering that 5 years ago. :R
Good Sam
Campgrounds listed with GS and a GS sign out front,...only to find out when you pull in they too said we don't belong to Good Sam anymore. And the best one is when you pull in and flip your GS card out and the owner tells you Oh, the discount is already 'built in the rate' Yea right. :R
KOA
IMHO the only CG that has standards and consistency across the US. Clean and I know what I am going to be pulling into late a night. No surprises.
AND if you have dogs they are VERY dog friendly. Unlike many other CG's.
Full timing on the road and Time and time again pulling into subpar CG's, dirty CG's etc I finally decided to exclusively stay only KOA CG's. :C