All 3 are excellant platforms.
I believe the AR10 is one of the best systems especially for accuracy and is a pussy cat to shoot. I have an AR10A4 that shoots 1/2"-3/4" groups all day with out a Free float tube and with a Bi-pod attached to standard handguards.
However that being said, In this day and Time If I were buying only one Id have to go with a FAL.
The quality of the Guns being built buy DSA is excellant. STG58 Kit guns built on their receivers go for under $950.00.
The quality and reliability is excellant and the ability to adjust the gas system gives it great versatility for different ammo, although I rarely adjust mine.
I have a DSA STG and an Imbel Kit built on an Imbel Gear logo receiver. Both guns shoot amazingly well and are VERY Accurate.
I spent $550.00 building the "Gear logo" Imbel and about $750.00 on the DSA Built STG58.
Now the Kicker In a day when M1A mags run $35.00 to $50.00 each and AR10 Mags run $60.00 Each, FAL mags are going for about $6.00 each yes $6.00 each for Styer, Belgium, Imbel etc etc. You can stock up for an eternity for a couple hundred bucks if you like. BTW FAL mags are one of the most reliable mags ever made I have shot thousands of round through "Beat- The - heck - up" mags and rarely have a malfunction.
Go to the FALfiles.com and check them out.
If you want High end and you dont mind the Bucks Go AR10
If you can Only have one and dont want to sink a fortune on Mags Go FAL.
BTW I have to disagree about FAL Accuracy, DSA is putting out some absolutely, wonderfully, accurate Rifles. Especially since the tack drivers have their free float tubes, check them out.
chuck