Have you thought about the cost of ammo for each rifle? As I see it, the AK will be the cheapest to feed, followed by the AR, followed by the .308's (most expensive round).
Have you experienced the recoil of each rifle? In my experience, a .308 bolt (the Ruger Gunsite) will recoil the most, followed by the M1A, then the AK, and the AR will recoil the least.
Do you plan on adding optics or shooting open sights? What range do you plan on shooting?
Good luck, let us know how you decide, and whatever you get, practice with it.
Ex - Navy, Persian Gulf Veteran. Loved shooting the M14, 1911, M60, M2