If I was building an AR based on fad, or popularity, it would have to be a Bravo Company, with Magpul furniture, a quad four rail, with Aimpoint. That collection seems to be as right now as it gets.
Since I am building, it's also what I won't buy. I learned long ago, watch the masses, do the opposite. It's not to say the products aren't quality. It is to say "Why buy what everyone thinks is adequate?" There is probably a better choice, often for less.
So far, I can avoid quad four rails, because I don't need to blow $300 for 48" of picitinny and I have nothing to mount on it, saving even more. I don't have KNS pins, because I bought a milspec lower and quality LPK.
I won't need a trap door on the pistol grip, because I have nothing to put there, or any reason to, just like my issue rifle for 22 years in the Reserves. Little parts, batteries, or a few CC's of oil isn't enough reason to weigh down the rifle, put it in a backpack.
I won't need a stock mounted mag pouch, or a redi-mag, because 10 rounds in the magazine is the legal limit. I won't need a light or laser, either, because as a hunting rifle, it's illegal in my state.
Tactical sling? No, I was taught infantry fieldcraft without a sling, and hunt the same - ready the minute I step away from the Jeep. I'm not handcuffing a dead whitetall or hog, and on a range, a shooter's sling is entirely different.
BUIS? Why not the primary system, or at least supplemented by a red dot, not an afterthought? And regardless of the model, any optic can and will go down. BUIS are largely non functional until made ready, which is weak. Better to have them co witness at least or separate if possible. A sight picture right now is better than fiddling around and praying.
Not having all the CQB tacticool stuff clamped on means about 4 pounds less weight, and not being seen a poser by LEOs - and others on the web.
Some forums actually have professionals on line.
