BCM, Daniel Defense, LMT, Colt. You get what you pay for. You'd be happy with any of these
It comes down to who makes their own parts, who makes parts for them and how well do they inspect each part.
At this point I doubt Colt actually makes anything anymore?
Continental Machine is from what I understand one of the largest manufactures of AR parts in the USA.
Also it would be good to Know the 2 largest manufactures of gun springs in CT probably supply most if not all the AR builders out there.
In the end it's a result your looking for that matters. If your looking to dump copious amounts of cheap ammo through a AR and hits on torso are good enough there's no need to spend more on a standard mil-spec barrel or buy a match grade barrel.
If your trying to put your shots in the X ring go for a decent barrel and good ammo.
I picked up a NM AR upper for a friend because he likes how mine shoots.
He then buys a cheap clamp on A2 rear sight....plastic elevation wheel and pot metal POS. Then runs cheapest steel cased through it....why can't I get good groups.... was the next thing out of his mouth.
Have fun with it Don't buy cheap just to buy cheap try to find a good deal on a known decent product