Normally my choice would be the AK, but based on information I recently received from an ammo dealer I think I would go with either the AR, or some type that fires the .308 ammo. The 7.62x39 is at the higest price it has ever been, and expected to go even higher.
The cost of firing the SKS or AK is being driven up by the requirement for ammo in the middle east. Iran is buying all it can get it's hands on in fear of war. Producers are selling to them because they are paying top price and paying in gold.
Bottomline, we may see a dry spell in 7.62x39 ammo, so but something you can get ammo for. There is plenty of 5.56 and 7.62 NATO (.308) out there, and the price is right.