What most shooters miss is tailoring the gun to what they need to do.
Too often discussions deteriorate into milspec vs the world, Brand Name fanaticism, and whether the gun will help you survive Life and Death.
Well, step back from the keyboard, take a deep breath, and think about it - for once.
If you need Job X done, it has specific requirements. In guns, that is putting enough bullet on target. Still a big range of jobs with the AR, just as there are a wide range of them, from sub 10" pistols to 24" varmints in target calibers. Most discussions go astray because the task is not clearly delineated - nobody really knows what the OP plans to do with it. And, neither does he. It's that sad.
Once Job X is known, then you can start sorting out what is needed. This is the order to do it, barrel and caliber, upper, optic, furniture, trigger, whether it's an AR or not. Match them to the job, in that order, and you get a gun that will help you succeed, not hinder you. Unlike what we see on the net, which is frequently bass - ackwards.
For most AR shooters, the 5.56 does fine for most of the list, until you get to hunting. At that point, state regulations apply. You WILL use an alternate caliber, no choice of that, just which one. How far your target is does dictate barrel length. It's a matter of imparting the required amount of energy to reach the outer limit of the job. Too many shooters pick a barrel longer than they need just to have an edge. What they need to do is rethink what power level they really want as an answer. 100 fps plus or minus is the ragged edge of range, and their marksmanship is likely to make more difference.
Most of us now use the A3 flattop upper. It's versatility for optics should be obvious. If someone deliberately chooses and A1 upper, it's limitations should be obvious, too. Mounting optics on it is at best a secondary role, and not the best choice. It's a retro build, not a modern firearm. What optic should match 85% of what you could potentially encounter FOR JOB X, not a what-if scenario. Far too many shooters get large magnification, when in fact they rarely practice at the extreme range and can't calculate bullet drop or estimate windage. Too much scope also means not finding the target quickly, as the field of view is so narrow.
Furniture is a huge market, and largely a waste of money for most shooters. Adjustable stocks may be nice, but the right length of pull for Job X is what most set them at. And some judicious shopping, instead of following the herd, would get them that. Too many are riding the M4gery fad, and spending $250 on a free float, when in reality it cannot and will not make the gun shoot any better than the inherent accuracy of the barrel. If it's milspec, it's 2 MINUTES OF ANGLE. You don't make it 1/2 MOA screwing on a bunch of doodads, and it's deliberately misleading to suggest it.
Same for the trigger. We've gotten spoiled with civilian target gun triggers on our bolt actions, in reality, the AR is a military knock about gun, and it's pull is set at 6-8 pounds because of it. Nothing wrong with cleaning it up, and a simple overtravel screw, which most better triggers have used for 50 years, will accomplish that. Because of the design, you can't simply install lighter springs and get the same reliability. It's a trade off, and shooter's need to be aware that light triggers on the AR are potentially capable of not hitting the primer hard enough. So much so, most tactical triggers built redesign the leverage of the pivots to compensate. On a standard LPK, that disadvantage remains.
If more AR enthusiasts would look at what they plan to do with the gun, and then select barrel and caliber, upper, optic, furniture, and trigger with a bit more common sense, there would be more appreciation for how it does the job. You can still spend $2400 for a dirt plinker or pickup truck gun, at least it would be made for the job, not some of the cross bred dachshunds/german shepherds posted up in ignorance.
Me, I built mine for hunting medium North American game. The ranges are from 25 to 350m. A midlength 6.8SPC 16" barrel, A3 upper, red dot optic, A1 stock, TD battle grip, rifle length handguards, GI FSB at rifle length. Foliage green. I don't sling up for a shot.
Specify Job X, build to it. If you want the latest techno toy, I can imagineer that, too. 14.5" .300 BLK., carbine gas, CMMG side plate upper with dual FA, Trigicon optic, Emod 5 stock, MIAD, KAC quad rail, Surefire suppressor and light. Don't forget the 100 round quad stack mags.
Easy when you do it right.