I'm not quite sure I understand your question - at all.
Are you asking what would be a good rifle to buy a large quantity of as preparation for SHTF scenarios?
I'd say an AK clone (like the SAR) would be good in that they're cheap, super-reliable and ammo is cheap and available now.
Are you asking which rifle would be easiest to get ammo and spare parts for?
I'd say the AR system, since the government has MILLIONS of them and there are so many domestic manufacturer of rifles and parts.
Are you asking a historical question about which rifle has been easiest and cheapest to manufacture - from a factory/process/raw material perspective?
I'd agree with Sukebe - a rifle using stamped parts is much easier to mass-produce. The germans really took advantage of this during WW2 and the G-3 is a direct descendant of that process.
Are you distinguishing between battle rifle and assault rifle, and civilian versions?
Are you sure you're talking about battle rifles? Those would be FAL, M-14 and G-3, using the powerful 7.62x51mm cartridge. Assault rifles (or the civilian clones of them) like the AK's and AR's are a different type of rifle, and not "battle rifles" per se.
As you can se, the answers are very different depending on what your question actually is. Help us out here.