ill repeat what i said on another thread
go with the armalite, they are readily availible, and there customer sevice is great so in the event that it does have an issue, the company will stand behind it, all AR maunfactures have issues from time to time, this includes colt, lmt and FN, no one manufacture is perfect,
the dpms is a better value and can give you the same preformence and reliability as the armalite, but the trade off is a one year warrenty opposed to a lifetime warrenty
another issue to think about is with RRA, is that as a trade off for using cheep mags, the original design was drastically changed from the original design, insted of feeding from the left and right, it feeds from the center, thus opening a new can of worms to a design that works well, but RRA has a lifetime warrenty and should cover there product, unless the design is dropped like bushmaster
even Kngihts is not perfect, although they may have great QC they have awful customer servirce as a result of military contracts
personly i would stay away from the RRA untill it is established in the market, just remeber when bushmaster was trying to sell it, I am sure in time it could be a decent gun, and will enjoy the same amount of aftermarket support as armalite and dpms
all in all, the dpms and armalite are great guns, its just what you feel is the best for you