Quoted:
The RRA uses FAL magazines, not the original Stoner AR-10 magazine design in production by Magpul, DPMS, CProducts, POF, Knights, LaRue, etc.. The RRA is a great rifle and much better IMHO than any factory DPMS 308, but every part of the DPMS can be upgraded with aftermarket parts, while there is very little that can be changed on the Rock River. There. aren't any other mags to choose from and nobody evengd makes a barrel for it. So if you want the better value on an out of the box gun get the RRA. If you want the ability to change, upgrade, and customize, then go with the DPMS.
Just my 2 cent but this says quite a bit. Out-of-box RRA is better but the $200 that you would save on the dpms will make you a happier owner of the DPMS. You WILL upgrade either that you get and the dpms can facilitate this.
I own a DPMS myself and it is great. My good friend has a RRA and it is great. I have extras and he doesn't...............Just sayin'