I am told that the AR-10 variants, when compared to my beloved M-14 and FAL clones, are: More Accurate, Easier To Scope, Cheaper, Mags Are Cheaper and More Abundant, Easier To Clean, Easier To Free Float (something you can't do with the other two), Easier To Add Accessories, Easier To Change Parts -> especially the barrels, Easier To Headspace, Has Better Ergonomics, Better Gas System, More Reliable, Better Availability of Parts which also means Easier To Maintain.
I have been accused of being a heretic for confessing this elsewhere, so don't chew my buitt too much.
Jarhead