Been a life member of the NRA for over 60 years, just an annual member of RMEF. When I took my life member of NRA things were a lot different. The NRA did more than lobby and ask for money, they actually helped shooters as their main duty. Today I get almost weekly communications from RMEF asking for money. I really don't see them doing a lot either, but they have a lot less membership. Take your pick!
If you become a annual member of the NRA they will offer you a life membership at a great discount after a while, that's the way that I got mine.
RMEF on the other hand is a very good organization. However like any large organization comes some corruption and RMEF is no different than most others. While I'll support their base cause as a annual member I refuse to go to any of their banquets after what happened at a couple of them near me.
With either one make sure that you have a large mailbox along with a good garbage can for all the request that they will send you.