First of all, let me welcome you to the fantastic forum of the MOC! We are presently members of RPI and Passport America. I would suggest starting with Passport and see if any other clubs are what fits your needs.
Passport offers 50% off camping at over 1300 campgrounds across the USA. One year costs $44 and that can be recovered in just a weeks visit at some cg's.
Now if I sound like one of their salesmen, I don't work for them. I DO get $10 off my next renewal by referring someone to them. If you do decide to join, use my members number RGI-0133942. Every time you refer someone, you also get a $10 fee towards your next renewal too.
As for the other clubs, they all offer a lot for each individuals needs, just take your time to check them out and this forum will be a great help! I am a member of Good Sam too and I don't know enough about the other clubs to give any honest opinions about them!
Check Passport out at
www.campsave50percent.com or call them at 1-800-283-7183.
Now, RPI costs quite a bit more and has a higher yearly dues, so we use this for more weekly stays. But I only pay $10 a night at some great resorts.
I highly recommend Passport as a starter discount club and one that you will stay with for many years.
Some PA parks allow the discount for your entire stay and some for only one night, these are usually the parks we use on our journeys from one place to another.
Go to the website and check them out, you won't be sorry!