As far as the stocks themselves, I've got two new Colt stocks, a Bushie new takeoff, and a Rock River new takeoff, and, except for the fact that the Colt stocks are in ziplock bags, you can't tell a bit of difference in any of them (I replaced the plastic door on the RR when I first got it, so that's not an ID factor any more).
The Bushie tube has just a bit of lighter coloring around the front end, the Rock River tube was black anodised all over, and only a Colt tube I have was grey colored all over. If thet coloring is dry lube, Colt and Bushie put it in the wrong place, because none of it is inside either tube.
The Colt buffer has a friction fitted rear bumper piece; the Bushie and Rock River pieces are split pinned at the rear.
For my money, get what's least expensive of any of the major brands. They're all essentially the same, with the exception of the plastic door on the Rock River stock.