HK, you make some great points too. But IMO there's nothing wrong with choosing an AK for SHTF scenario as much as an AR. I really have not had trouble stocking up on 7.62 ammo at all; its even available locally now in my LGS while I still cannot find 223 ammo anywhere in stock except online.
Weight is a personal issue. Of course 7.62 is heavier per round, but I would admit its also heavier hitting than a 5.56. Each caliber has its pro's and con's so choose your battles wisely, so to speak. If you prefer a lighter load-out then the 5.56/223 would be the better choice. But I really don't have an issue carrying the same amount of 7.62 if it came to that. A smaller/weaker person might be better off with 5.56.
Well I don't consider it a feat of strength I think its more about a true survival situation. A natural disaster or whatever made you have to LEAVE, if its that bad, your car will run out of gas eventually, than your on foot. I want my rifle for protection as well as maybe even hunting. However I do want a decent amount of ammo, but I don't want it to be the ONLY thing I have either. A person say has a set limit of weight they can carry. It is different for every person sure, but the distribution of that weight is what is important. I don't want 95% of it being ammo. The more weight I can save per round, might mean extra weight being taken up for food/water/shelter/medical what have you. Lets face it, I can carry more twinkies having 300 rounds of .223 ammo than 300 rounds of 7.62 ammo.
7.62 ammo isn't all that HARD to find pre-panic, but your simply lying to yourself thinking it is as EASY to find as a .223 or 5.56, specially given the SHTF scenario people are referring to. You will have national guard units showing up, there will be in influx of .223 and m16's even more so than what you could already find.
Also your AK only packs more punch out to a few hundred yards, than the 5.56's better BC takes over and will carry energy better/further than the 7.62x39.
I love my AK and my Saiga 12, don't get me wrong, I just don't seem them as being my go to solution, but I am fine to disagree as I see no reason NOT to choose an AK either, I just have my reasons for preferring the AR, and unlike most on the interwebs I am not stubborn enough to think that only my answer is correct.