My $.02
Armalites are built to very exacting tolerances and therefore can be sensitive to dirt and ammo choices. They usually require a bit of break in and ammo experimentation.
DPMS rifles are a touch looser in their machining and they arent quite as finicky ammo wise.
Both like to run with a wet bolt carrier.
Armalites are machined from forgings whereas DPMS are machined from billet. As a result the Armalite will have a more refined appearance and is a touch lighter.
I have worked on both and have yet to come across a problem that was not a fairly simple fix.
Rock River has a .308 platform that uses FAL mags but I dont have any real time with one other than looking it over. Seems well built.
Not sure on the LWRC- too new to make a call on them-I have yet to hear any feed back on them.
I myself have a DPMS TAC20 with a J&P trigger, Magpul PRS and Nikon optics. It will outshoot whatever my eyes can see and I have out shot an Armalite SASS with it.
For about 1/2 the cost.
Maybe one of these days I will change out the barrel and bolt/carrier. That is where the accuracy in the AR platform is....