Back in the olden days, we humped our own M-14's and ammo, but you had to sandbag them to hit anything with them on full auto, so most of the M-14's issued were missing the selector and our creed was, "one shot, one kill." Let the M-1917's and BAR's handle the full auto glory.
My M1A1 Ultra Match (M-14 semi) was my shooter of choice when using a service rifle in DCM high power competitions. My best position was 200 yard rapid fire (about a round per second) from a setting position, from which could shoot Grand Master scores with it, but unfortunately my standing offhand sucked, so I never won a tournament.
As a civilian I've owned a HK G-3 a FN FAL, both sweet, and an AR-15 SP-1 but they came out with the M-16 after I was discharged and I've never shot one or handled a XM177E2.
I agree that for reliability under extreme conditions versus accuracy, the AK-47 is the weapon of choice. Sort of the Honey Badger of assault rifles.
My AR-15 SP-1 was a tack driver but was easily fouled and didn't have the forward assist that they added later, so was fussy with ammo.
Hard to beat the M-14 for breaking falls when diving for cover and when parrying or delivering butt strokes. You treat her with respect, she will take care of you!