People don't generally realize that the "NRA" is actually 3 separate organizations. There's the NRA that everyone is familiar with that supports hunting and shooting sports, there's the NRA-ILA (Institute for Legislative Action) that supports 2nd amendment rights, and there's the NRA-PVF (Political Victory Fund) that supports the best incumbent (based on his voting record) in an election.
GOA is a fine organization, but so is the NRA. I have a lifetime membership in the NRA but only send (additional) money to the NRA-ILA, which supports 2nd amendment rights (but NOT to the NRA-PVF).
It's not an either/or decision, I'd encourage anybody to join both.