Squantos and Travis, kindly throw in your own two cents worth. I tend to agree that the full-length 20-inch barrelled AR is the way to fly, both to get as much power and accuracy [sight radius with iron sights] out of the 5.56mm cartridge and to maintain as long a gas tube as possible for enhanced reliability.
I've got both a 1:12 twist barrelled M16A1-equivalent AR semi and a 1:7 twist M16A2; of which either is used according to the ammunition available, 55-grain M193 ball or equivalent with the 1:12 twist or 62-grain M855/ SS109 or heavier bullets with the A2 1:7 twist. Also, the 40-grain lead bullet of the .22 long rifle is much better suited for use with the earlier 1:12 twist barrel, if the use of a .22 conversion kit is of as much interest to you for additional training or versatility's sake.
The M16A2 configuration is to be chosen for use as a 600-yard match rifles, if that's among your intended purposes, and that's what mine is mostly meant for.
My M4 shorty version can't really be called an M4gery because it's really closer to the configuration of the Canadian Diemaco C8FTHB. Since it's not one of the longer-barrelled versions you prefer, it's likely of less interest to you, but it is useful to me both for evaluating ammunition intended for the shorther 14.5 and 16-inch barrels, and as a testbed for evaluating various Picatinny-rail mounted optical and electrooptical sights.
So far as manufacturers go, there's really very little difference between lower receivers, and an accurate and reliable gun can be built on a fairly unimpressive lower receiver, as witness the various guns built on the cast Sendra, Essential Arms and *Coal City* lowers a decade and a half ago. Both polymer and stainless steel lowers have been around, but they are of course not the norm. The old SGW lowers [now Olympic Arms, which began as Schuetzen Gun Works\ were pretty good when Hank was building them in the mid 1980s and early 1990's, and I'm also fond of both the machined billet component lowers and complete rifles made by SI Defense in Kalispell, MT.
A local gunshop has been going through the Hi-Standard ARs as well, happy with them due to reasonable cost [which their customers like] and minimal after-sale returns for replacement or repair, which their gunsmith likes. I'm fond of them as well, and have reccomended one to my fiancee as her pick for an analogue to the M16A2s with which she was trained in the USAF, she having tried a Colt CAR-15 and not liking it, preferring folding stock versions of the AK74 for her uses in the carbine role.
Additional info: check the articles posted *here*. There's some solid wisdom in some of the response posts here and there.
I bought two bushmasters m4gerys. One for the house an one for thee gun matches. Both dressed identical. About 15,ooo rounds thru each since I bought both on same day.
Truck gun is a TRW based M1A with spare mag on the stock with a unertl 10x a Marine ummm...gave me....:o)
77gr black hills for the AR’s an 168gr Federal Match for the M1A....
My boss loans me an Hk 416 for work....very reliable rig.
I win the lotto I’m buying the semi auto variant of that in 6.8.