Considering that by your own admission, we were discussing these rifles in the terms of civilian ownership, automatic fire hardly seems relevant to the discussion. All three of these battle rifles were eventually issued with automatic fire capability removed in some versions even as military weapons.
Between the AR, FAL, M14, AK, and G3, only the AR has its charging handle in a more awkward position, IMO. Then there is the lack of the paddle style mag release on civilian rifles, which again, as they are the rifles being discussed, are absolutely relevant to the discussion at hand. The safety on the M14 is ambi. It is the only rifle to offer this feature as a standard item. Meanwhile, the safety on every G3/HK91/clone that I have handled has seemed unnecessarily high and farther out of reach than it needed to be, and I have pretty big hands. The safety on the FAL and the AR both seemed more accessible to me.
In terms of sights, I haven't messed around with them much but I fail to see how the HK sights have a single advantage over the sights of either the M14/M1A or the AR--not in speed, not in precision, not in adjustability, not even really in durability. Not a single advantage. Without peer? Hardly. They are adequate, but not exceptional--a lot like the entire rifle, really.
And those modifications I listed for the civilian roller lock rifles are modifications that must be done to make the rifle in comparable to the standard M1A. You can buy a standard M1A or even a Polytech or Norinco and not have to do a single thing to it to get it to be on the same level in terms of reliability, durability, or accuracy, as an OTB HK.
Now yes, there are a lot of modifications that can be done to the M1A, but none of them have to be done to compare to the quality of any single component or function of the HK rifle. Not the gas bedding, not the NM mods, not unitizing the gas system...
And even with these mods, you're still looking at a rifle at least as capable as an MSG-90 or PSG-1 for hundreds, possibly thousands of dollars less.
"...nothing says 'I WILL shoot every last one of you before you have time to reconsider your poor choices in life' like an AK."