I'll take a .22. You can carry a ton of rounds, kill up to medium sized game with it, pretty accurate, greater range than a shotgun, less weight and more ammo than a AR, smaller sized as well.

now if this is just for survival, that is what I will go with. if it is a SHTF situation where I may be fighting off looters, bad guys, zombies etc...then I will opt for my AR.

of course in reality i will have more than 1 gun, and plenty of ammo for everything.
I would probably grab an AR, 10/22, .45 or 9mm pistol as well as a 12 guage, and plenty of mags and ammo for each which I handily keep readily available!