I have the DPMS. A few things to consider. They have several models. The target models with bull barrels don't have bolt forward assists. This can be a pain in the butt if the rifle jams. Because of the AR's design if the rifle jams with the bolt not moving fully forward into battery the gun is stuck bad. You can't break the action. Without a forward assist I needed to find a small allen wrench, put it in one of the holes in the bolt and drive it forward by pushing and pounding on the allen wrench.
By the way this happened the first time I was shooting the rifle and it was in a very very harsh desert environment with blowing dust. Since then I've used a little more lube (the FN doesn't need as much as the AR in my experience) and try to keep it out of blowing sand and haven't had a problem.
Also the 18" barrel'd rifle is very heavy and puts out a big big flame, as there is no flash hider on it. Nor is one likely to find one to fit the 3/4 of an inch barrel.
On the other hand, the thing is a tack driver. I can group a few inches at 300yards all day, with semi-cheap ammo. Also, it's very pleasant to shoot.
The newer ones, that look like the current issue army rifle, have forward assist plungers, and dust covers. The target ones don't have dust covers.
If I had it to do over I'd like the top end with those features. I'd probably go for the 24 inch barrel to get the flame down to size I do love the accuracy and even the SWAT guys with their $3000 Accuracy International rigs were pretty impressed with the groups I was shooting at 300 yards.
One reason I like the DPMS over the Armalite that the magazines are pupose built for it and work well. (Except the original plastic ones, they are pretty bad) The Armalite uses modified M-14 magazines. (The Bushmaster used FN magazines.) The DPMS magazines interchage with the ones for the Stoner SR-25.
The AR-10 is a really great gun. Despite the teathing problems I would buy it (or another variation) again. DPMS has been excellent to deal with. They sent me replacement mags at no cost when the steel ones came out.