I have 2 post-ban AR15s -- a Colt Match Target HBAR and an Armalite (nee Eagle Arms) Golden Eagle. Both have been reliable. The Armalite is a better gun (but also more expensive). The Colt's front sight and rear sight have to be adjusted well out of the middle of their range in order to sight in the rifle.
The standard single-stage trigger on almost all ARs basically sucks. I strongly recommend that you spring for a 2-stage national match trigger. There are several available, including Armalite (which I have), Jewell, Milazzo-Krieger (supposedly the best, but expensive and nearly unobtainable).
If you are going to compete in CMP service rifle, then it is cheaper to buy a rifle that is loaded up to begin with (national match sights, national match trigger, free-float tube, match barrel, etc.), then to buy a rifle and start swapping out parts.
I recommend either Armalite or Bushmaster. Given my limited experience, I can't recommend Colt. I've heard good and bad things about Olympic Arms, but have no direct experience. YMMV.
M1911