The .308 AR platform isn't standardized like the AR15 is, so you're looking at a range of rifles that are similar in design but partially or completely incompatible in their parts. So your ability to upgrade later is more limited, and you're basically buying a proprietary design that may have limited parts options, instead of a military-based design with dozens or 100's of parts options.
For $1k or less you're looking at the DPMS and not much else. It's actually a pretty good rifle as long as you don't expect "mil spec" type details (barrel steel, testing, etc.). Compare it to other semiautos that aren't derived from a military design and it's a good rifle and relatively modular.
Step up the price a little and you have options from Armalite, RRA, and S&W, with S&W being the newest by far. It may also be the best quality wise but that isn't proven yet. If you want to shoot tiny groups at a bench, DPMS and RRA have better affordable free floated options.
Go up towards $2200+ and you get some additional nice options like the Colt 901, LMT MWS, and Larue 7.62 rifles. I'm guessing this is outside of what you want to spend.