which card to get AAA, Good Sam, KOA, RV America

Good Sam and AAA are widely accepted for discounts.
And many will give a senior discount, even without AARP card.
And if you stay at KOAs (we often do) then that is a good card to have.
We have Good Sam, KOA, and AARP cards.
We pretty much just try to get what ever discount is available at where ever we stop for the night, rather than seek out specific parks that accept certain memberships. If we spent months on the road I may be a little more particular.