I have owned or shot all of the rifles you listed.
1) G3: great gun, mags available, no frigging gas adjustment to fool with, just load & shoot. Groups are a bit to be desired though. Still have mine, Federal receiver.
2) FAL: decent gun, frigging gas adjust to fool with. Every time I changed ammo brands I had to readjust, a PITA. Sold mine.
3) M1A: had the real thing in the Marine Corps, shot many civvy versions since. Good rifle although accuracy with the standard set-up may not be perfect. Op rod problems are a bitch if encountered.
4) AR-10: just bought an Armalite. WONDERFUL gun!! Recoil is almost non-existant, great accuracy. Mags are seemingly a bugger to get in 20rd sizes. Conversion kits from Armalite seem to be the way to go there. I'll not part with this one!!
Hope this helps.