Wow you do have some great options Arch.
What rifle is most reliable with only field maintenance?
What rifle do you have the most ammo and mags and a system to carry said ammo and mags?
Where do you live? will long shots say 500m plus be a possibility/necessity?
The AR, Ak, and SIG (mabey the mini-30) will mostly be the lightest to carry and therefore you would have less difficulty covering terrain steep or flat.
The M1A and FAL are no doubt battle rifles, but they weigh much more.
Is oal an issue, Will CQB be a possibility? in and out of buldibngs, a boat, a car etc. if so the shortest one you got may be best.
In a post-apocalyptic world (your area where you live) what round will be easiest to find 7.62x39, .223, or .308?
Dose the AK, Mini-30, FAL, or SIG fold? to be hid in a backpack or something.
If the M1A or Mini-30 are wood stocks then with lower-cap mags they will look less (evil) and not draw unwanted attention.

Tough choice.