Of the manufacturers of AR 15, how do they rank in quality?
ABC: ArmaLite, Bushmaster and Colt.
Very comparable among these three, but everybody likes their own brand. Armalite is not the same Armalite that originally created the AR-15 (they just use the name) but they're not bad. Some people like Colt, some like Bushmaster.
Colt will not sell post-post-ban Law Enforcement weapons to non-LE. You need a department letterhead to get one from Colt, so Bushmaster sells over 2x the civilian sales as Colt. All "civilians" can get from Colt is the Match Target variants (like the M-16A2 and A4) but not the carbines.
Knights Armament is offering their SR-15, which is a much refined version of the AR-series. You pay big bucks for Knights rifles, but they come with everything. Quality is very high and the price is equally high.
After these, there are lesser brands like Rock River (not bad, but I've seen some troublesome rifles) and others. Nearly everybody is offering an AR these days.
I would recommend Bushmaster because they offer the quality, the models that Colt won't offer and you can actually get their rifles.