Two pages of the usual.
What do you want this rifle to do? Just be an AR15 sitting in the closet? Or do you plan to shoot it? If so, where and how?
Those questions don't get asked often enough. The OP owns guns, has some from what I gather, the point of having the AR is to fill a specific need better than what some other gun will do.
The main qualities of the AR: 1) light 2) uses medium calibers easy to shoot 3) much more accurate because the barrel is mounted on an extension and can be easily free floated 5) factory stock will shoot 2MOA in most cases, which is good enough for most North American game from woodchucks up. If smaller, more accuracy is needed - but the calibers available can still do the job.
Are their lots of choices, yes. BUT it's not confusing when you specify exactly what you want the rifle to do. Don't look at choices - look at what you want it to do. Then pick features that support the job.
You don't buy a two door sports car to haul three kids in car seats around. You get a mini van. So, the effort to narrow down the choices on the AR15 is What target, what range? What target tells you what physical size it's going to be, which determines the minimum MOA it's got to shoot, and what range tells you how much bullet mass you need to hit that far out. That will quickly narrow down the calibers with the delivery.
A bull elephant at 1000 yards, nope. But a bull elephant at 50 paces with a .458 Socom or .50 Beowulf, possible. A rabbit at 1000 yards, might even stick to 5.56, but 6.5Grendel would deliver better ballistics.
In a carbine with barrels as short as 8" - really a pistol - then 6.8SPC. It's already an issue weapon fielded with the Saudi Royal bodyguards. And a LOT of ammo is coming around because of it.
"I want an AR15" shouldn't back somebody into a corner getting something they don't want or need, but at least the AR can be easily changed to what will work. Just specify what target, what range, and you get the most versatility of nearly any gun made with parts available from more than just one proprietary vendor. Literally dozens make parts for the AR - just be specific what you want. That will narrow it down tremendously.
Of the two choices, the S&W for cash right now will do. It's a good middle road choice.