With modern metallurgy, and manufacturing techniques, does an AR barrel have to be cold hammer forged and chrome lined to by a "good" barrel. New nitride treatment seems to be the norm, but is is as good a good ole chrome? 4140 vs 4150 is one really that much better than the other? Not talking gucci stainless.
CHF using one of the newer steel formulations like A&D and then chrome lining are going to net you the longest barrel life. Cut rifled stainless with one of the new alloys like "BB" from Bartlein and the like will net you the best accuracy.
For CHF barrels, I really like Daniel Defense and Colt Canada (Diemaco).
FN makes some excellent barrels, but I am just not the most impressed with them as there has always been a lot of reamer chatter in the ones I've scoped, as well as the fact that they cut their chambers in instead of forging them in. This leads to a bit of variance as well as the chrome eroding out of them sooner than DD and Diemaco barrels. Just my small sample of experiences.
H&K makes some excellent barrels using A&D steel and their chrome lining processes, but they are much less accessible to me, and I don't like piston guns on AR architecture, so there's that.
With ammo that I prefer (Browntip and MK262), I have found DD and Diamaco to be 1.5-1.8moa barrels (10 shot averages), even using improvised field positions and LPVOs. This is plenty for me, but if you want precision, Bartlein 400MODBB barrel chambered by someone who knows what they are doing such as Craddock, etc. is what I'd go with.
If you are looking for a COTS solution and can find one, a Colt CR6724 is an excellent piece if you don't mind using lighter bullets in deference to its "1/9 twist" (they are actually typically a 1/8.5" twist and will tolerate heavier stuff than a 1/9 "should"). I have put thousands of rounds through one and it's a 0.9-1.1moa gun using ammo it likes if I do my part.
The formation and material of the bore is more important than the treatment or coating of the bore.
