This is a question that is asked so often, I've actually created a "stock" answer...although the variations usually include the G3/PTR91 and M1A. While this answer isn't targeted specifically at the AR variations you ask, this is my "stock" answer.
Here are the rifles I'm using for my opinion...don't own an AR10 so using the AR15s as a proxy.
Cold War era battle riflesCETME, 7.62x51mm
PTR91, 7.62x51mm
DSA StG58A, 7.62x51mm
DSA SA58, 7.62x51mm
Egyptian FN49, 7.92x57mm
Springfield Armory M1A Loaded, 7.62x51mm
WASR-10 AKM, , 7.62x39mm
Yugoslavian SKS M59/66, 7.62x39mm
AR-15 based riflesJ&T 24” varmint upper on DPMS lower, 5.56x45mm
CMT upper, 18” WOA barrel on AeroPrecision lower, 6.8x43mm SPC
J&T M4-gery upper on DPMS lower, 5.56x45mm
WOA DCM upper on Rock River lower, 5.56x45mm
Olympic Arms upper on DPMS lower, 9x19mm
In the end, you need to pick the one that fits you best and you can shoot the best. For me, that is the FAL. M1A would be a close second.
Here's my synopsis of your choices:
M1APro
- reliable design
- full power cartridge
- very comfortable (for most) stock
- can be quite accurate
- great sights
- safety is convenient location in trigger guard
Con
- scope mounting is awkward over the receiver
- field stripping has lots of part/not straightforward
- can't be cleaned from chamber side with a rod
- expensive mags
FALPro
- reliable design
- full power cartridge
- extremely good ergonomics
- cheap mags
- extraordinarily easy to break down, field strip, clean
- adjustable gas system
Con
- Sights are adequate but better A2 style sights exist
- Triggers not known to be great but they can be improved
HK91/G3/PTR91Pro
- reliable design
- full power cartridge
- cheap mags
- somewhat easy to break down, field strip, clean
Con
- Sights are adequate
- No bolt hold open
- Abysmal ergonomics - safety selector is near impossible to reach, cocking handle is in terrible place, mag release is hard to reach
- Triggers are absolutely horrible but they can be improved
AR-seriesPro
- proven design
- full power cartridge
- fantastic ergonomics
- extraordinarily easy to break down, field strip, clean
- very modular
Con
- Expensive mags
- Not as common...but still plenty of parts around
- Charging handle is in a silly place
All this said, I think the FAL is the best of these. If you want the AR for the ergonomics, you won't lose with that rifle. You'll hae to make a choice on long vs short barrel...on most of my rifle platforms, I have both...sometimes I like the velocity, sometimes I like the compactness.