As far as I know, RRA uses the same components as Colt and Bushmaster, from Continetal Machine. Oly makes their own stuff.
I keep hearing that RRA sure knows how to assemble a rifle. Oly doesn't do chrome lined barrels, RRA does.
I prefer Oly's, but if I was going to buy anything else, I'd go RRA.
The SUM (Stainless Ultra Match) barrels from Oly are SAAMI, they are broach cut with tight chambers, 4 lands/gooves target barrels with a 1:10 twist (1:8 optional).
All their chrome moly barrels NATO compatible.
Oly gives you the option of ordering a full blown custom setup (to customer-supplied specs) with MaxHard receivers, BlakTac armored bolt carrier assemblies, Ace Stocks, FIRSH rail handguards, fluted barrels or M4 contour, alternate calibers and a variety of bells and whistles. I spend the weekend playing with Oly's latest toys and what little publicity there is doesn't really do the construction or finishes justice.