here's my .02. I use a Colt 6920 (effectively a semi-auto M4) and it is great. I have a friend that has a DPMS carbine and he's spent a good bit more money getting it to shoot like my colt. He can outshoot me now, but not with the heavier bullets (75 grs+). He also built a 20" bull barrel flat top from Model 1 parts. I've handled it, but not shot it. I have a LE friend who has a RRA standard A2. I've checked out the Bushmaster, Rem R-15, and Sabre. All are good, but the devil's in the details. Colt, Sabre, LMT are about the only ones that are truly mil-spec throughout. What that means is they are less likely to come apart, which is not really a likely situation for a civilian anyway. Bottom line, most are good. For mid-priced rifles, the Bushy and the Rem are great. The higher end ones (Colt, Sabre, LMT) may last longer, but really won't outshoot the others. I wouldn't disregard the carbine (short handguard 16" barrel) either. They are very handy in a vehicle and shoot as well as a 20" barrel. Unless it's a bench/varmint gun, the heavy barrels make them real muzzle heavy, so I personally don't like them for a defense or hunting rifle in an AR. The Remington seems to fit your criteria best and as far as I know it's well made and should serve well.