If you want to stay under $1,500 ... the DPMS would be a better choice. I have friend who owns a DPMS LR .308 24" and another friend who owns a Armalite AR10.
Both are good guns, but my friend with the Armalite paid $1,600 the gun, and the other friend paid $1,100 for the DPMS.
The Armalite used modified M14 mags, and are not cheap ( however have come down in price you are looking at around 40 to 50 bucks)
The DPMS uses SR25 mags and during the AWB these mags were VERY expensive $150 bucks or more.
Now the AWB is gone DPMS is selling these mags for $30 to 45. (Stay away from the DPMS plastic 10 round mags. They were junk.
If you are looking for a 16 or 18" .308 AR with a flat top and collapsibe stock check out the DPMS AP4. You can the whole gun with four way rails and BUIS for $1250 to $1350.
The Armalite will cost a lot more than that.
Chris