[travelin texans]

From our experiences get both the KOA card & Good Sam's.
KOAs are typically more expensive than others, but if you have kids or grandkids with you a good many KOAs have entertainment for them. After you've accumulated so many points KOA will upgrade you to a VIP membership giving you a 15% discount.
GS gets you discounts at all sorts of campgrounds across the country from large to small some with lots of amenities others with none. Plus you get discounts at Camping World & Flying J/Pilot fuels.
Neither will get you discounts down to the price of state or local parks though, but usually GS gets them cheaper than any KOA even with their regular or VIP discounts.
Passport America is another way to save 50% on campsites especially if camping during the week. Just be sure to check their blackout dates before hand, seemed we could never stay the right day to get their discount, it was always yesterday or tomorrow.