Noveske is in the same 3k+ price range as a KAC. Armalite uses their own mags, which are pretty pricey compared to a p-mag. This is why I don't recommend Armalite. Between the DPMS and RRA like you originally asked, I like DPMS. Their "AR10" seems to be a lot higher quality then their AR15's, and they use a very common mag on a common platform, SR25. The RRA seems to be plagued with feeding problems associated with its use of FAL magazines.
What madcratebuilder said about interchangeability is correct, do your research on what manufacturers can be provided with aftermarket parts. I know that DPMS just changed receiver heights on their flattop .308s which may take a little while for others to "catch up" on, but for the meantime you can get several free float tubes from DPMS.
Bottom line... if you have 3k+1k for optic/accessories to spend, get a KAC or Noveske. If you don't, like me, get a DPMS and slowly build it were you want it.
When I shoot out the factory barrel I will replace it with a nice match barrel. Even though the one that is currently on it was shooting sub MOA after the first 50 rounds using surplus 7.62x51.
I wish more companies were building them in .308, but unfortunately we are stuck with 4 or 5 companies and a limited aftermarket support for now.