I have alot of range time with the M1A, FAL, and SAR8 (Springfield G3 clone.) I have no actual experience with an AR10 (althought I am quite familiar with it's little brother)
Here's my train of decision...
Since I'm not a fan of the DI gas system, I can exclude the AR.
The HK is a great gun, but the balance is a bit off for me.
So it comes down to the M14 and FAL. It's a very close call, but I have to vote for the FAL, by a nose. The pistol grip and left side charging handle make the difference.