Save getting an AR for some time down the road, if they and the ammo are ever available at reasonable prices again.
I recommend something in a 9mm carbine configuration like the Ruger takedown semi-auto that takes Glock magazines. Does not attract the attention that an AR or an AK variant does, and the muzzle blast will not be so disorienting when firing inside a car or a room in a building. Also, 9mm ball penetrates barriers like auto glass and car bodies better with the bullets remaining relatively intact after pass-through.
Sure, the 9mm has a more curved trajectory than 5.56 and 762.39, but it does pretty good out to 200 yards, and in a social unrest situation, you are not going to be engaging targets much beyond 50 to 75 yards anyway. ( Assuming that is the purpose you have in mind )
Actually, a lot can be done with a .30-30 or a .22 LR. The ammo is easier to come by too.