well since the two main companies that make the M16/4 rifles are FN Herstal and Colt I would recommend those first. however I dont really like colts prices and FN Herstal does not sell an AR15 to civilian markets. however if you feel up to the task of building one yourself. palmetto state armory has a proprietary group of build kits which are almost entirely FN Herstal parts so you will essentially be getting a milspec AR that's been restamped for PSA and you'll get it for a fraction of the price of a colt.
the upper reciever, bolt carrier group, barrel, gas block+tube are all completely assembled. the lower recievers need some assembly but there are plenty of vids on youtube and the like about proper assembly and it's not every difficult.
a completely milspec colt is going to run you about 1200-1400 dollars, the palmetto state kits will cost you about $600-700.
I often take the stand that milspec isn't everything and that in most cases a good economy model is all anyone ever needs but if I ever decided to go with another 5.56 AR it would be a PSA build