If you or the wife is age 62 or over - the federal Senior Pass is essential. One $10 lifetime fee for big discounts at federal campgrounds. Even if you don't camp in National Parks - the free admission for one park one day will pay for the card.
Passport America has the best return on investment of the group. You have to work hard to not make back your membership fee in discounts in the first couple uses of the card. But it is really for traveling - those one or two night stops between destinations. If you don't travel much, it isn't worth the effort.
AAA and AARP pretty much duplicate their discounts at restaurants and motels/hotels across the country. Depends upon your age.
One area where I think many folks get duplication is with 'Roadside Assistance' services. FMCA and Good Sam have very good RV focused programs available. AAA has a great program, but really doesn't like RVs in my experience. Guess what - when you make a call to any of the roadside assistance programs - the tow truck company contacted by all three is the same.
Choose one and don't pay for the other two.
Yes, most RV parks have discounts if asked, and it's pretty much the same for any card, program.
KOA is a bit different because they have their own card/ program. If you use KOA, it is definitely worth it.
I consider Escapees a requirement for full-timing if your full-timing includes traveling. Even if full-timing is staying in one or two places for the whole year - Escapees provides services and information you really need.