I've got enough rifles for my immediate and local extended family, should the need arise - both 7.62x39 and 5.56NATO (and in a couple other calibers). I figure: better to have a little diversity so that in the event of ammo unavailability/scarcity, we've at least got something for defense. .22LR is always likely to be available for food acquisition.
As for 7.62x39, I'm not fond of the AK. Yes, it's durable, but it's also heavy for small people without a lot of upper-body strength (ie women and children). And, personally, I have a difficult time shooting one without an American-made stock because the "Russian bloc" stocks are too short without winter clothing; combined with the general setup of the AK, I find it awkward. Not so much the case with the SKS, which feels more natural to me.
I'd like to get a .308 AK for those "reach out and touch something" situations - a little more firepower in the same basic package. The price on one is close enough to that of a 5.56 AR that it's justifiable now, and a .308 AR is still lighter than an M1A. IMO, weight is a big factor for SHTF.
There are also a lot of other viable options for 'diversification' such as shotguns - like the Saiga 12 or a common Mossberg.
A very real SHTF scenario is a war with China. I think that they would nuke us first then invade, probably in the west coast area or possibly thru Central America. Their forces all use an AK47 variant. During the vietnam war, the clack clack clack sound instantly identified an enemy as firing an AK47. I would much rather be firing an AR15/M16 in this type of scenario as I would be recognized as a "good guy" by the sound of my rifle.
In that (less likely than several other scenarios) scenario, you'd soon be hard-pressed for ammunition for your AR, even if you were well-stocked. In such a fight we'd likely be over-run and killed off pretty quickly due to sheer numbers, I think; but, failing that, we'd also quickly pick up the enemy's weapons when we're able.
Also, if you're drastically out-numbered, I can see a tactical advantage to using the enemy's weapons: the enemy might not identify it as hostile fire until they come under direct, personal fire (especially if there's a secondary front with ARs or similar).