I'm a member of the NRA but don't always agree with their methods. With that said, I'd rank the mags in this order:
1. American Hunter
2. America's First Freedom
3. American Rifleman
If you are a hunter, American Hunter is your best choice. If you like the legal side of firearms, America's First Freedom is pretty good. It is heavy on the propaganda but I enjoy it. American Rifleman usually has a good article or blurb, but in my opinion it's the weakest of the three.
It should be noted that each mag carries some of the same articles each issue so there is a lot of bleed over between each mag.