I currently have only one AR15. When I was in the market for an AR a little over three years ago, the most important thing at the time was to make sure I got a brand name AR.
As luck would have it I got a Colt. It was NIB preban when I got it. The model is a 6601 "Sporter Match" w/ 20" Hbar barrel and a 1/7 twist and A2 upper receiver. So far I've only shot 55 grain 5.56 Winchester Q3131a ammo. BTW,the Q3131a is made by IMI for Winchester. Although this is a regular production rifle and not a special production or a gunsmith built target model this rifle is still very accurate. The twist rate will work with 55 grain up to about 77 grain.
I also have a complete flattop upper w/ gov. profile 20" 1/7 barrel for it to use with a scope (gov. profile is thinner under HG's than Hbar). The only mod(so far) was putting a G27 grip on it. I tried an Ergo grip but the G27 is a little larger in width and it fits better.
When I was shopping for an AR I was going to trade (an AK47 folder) since cash was in short supply. Originally I had a deal pending with a guy who had a Bushmaster but he reneged on the deal after he agreed to go through with it. After more games and "tire kickers" wasting my time, a friend said a buddy of his had TWO Colt AR's,and yes, he would gladly trade for a AK.
To this day he is still happy with his AK and I am quite happy with my AR!!
Although I love my Colt ,there are other brands out there that are just as good such as Bushmaster and Rock River but without the political baggage.
FYI: Colt and Bushmaster use 4150 steel for barrels, all others use 4140. More importantly make sure you get a chrome lined barrel. They last longer and are easier to clean. Non chrome lined barrels are generally a little more accurate. Olympic makes a barrel marked as SUM. This is their ULTRA MATCH barrels many rave about.
HTH
CrazyIrishman