For me, it was a toss-up between 2 Colt models (6920 and 6940) and whatever Bushmaster model OGC had on the wall next to them. They had 2 6940 models: one gas impingement, and one piston driven.
The furniture is a big factor for most people. It's one reason I went with the floated quad-rail hand guard on the 6940 vs. the standard carbine AR15/M4/M16 A2 style hand guard w/A2 sight & gas block combo. The barrel I picked was already free-floated, which by most accounts increases accuracy. The A2 hand guard didn't offer rails, so it would have been another $100-$200 to get a suitable quad-rail hand guard, which was what I wanted.
My favorite hand guard is the VTac Alpha, which has a picatinny rail on top, and small rail pieces you can install in any of the vent slots. The hand guard allows for a free-floated barrel, is light, and is super easy to install.
Colt actually did something relatively recently that I think was a good move. They started offering the 6920 OEM models. They both come with no furniture, allowing you to pick your preferred butt stock, hand guard and trigger guard. OEM comes with the fixed A2 front sight/gas block, and the OEM2 has a low profile gas block to allow free floating the barrel.
There are a few designs for AR furniture to consider. Those I mentioned are just a couple. You can pick from MLOK hand guards for mounting accessories, minimalist butt stocks, pistol grips with storage compartments, vertical fore grips, angled fore grips, fixed front sights, folding sight sets, adjustable gas blocks, various finishes for the Bolt Carrier Group, and, of course, there are a large selection of "novelty" features like receiver engravings of logos/pictures for Zombies, Pirates, Infidels, etc, etc.
The point is, there are lots of ways to customize an AR. Buying a factory gun requires a little research into what the factory models offer and what you intend to replace after purchase, if anything. Manufacturers sometimes offer variations on the same model with simple furniture differences, like a Magpul version. It'll have the Magpul trigger guard, one of several Magpul stocks, one of a couple Magpul grips, and a Magpul hand guard.
The Colt OEM models offer a lower price for a Colt AR allowing (requiring) you to buy whatever furniture "trips your trigger." If nothing else, that delays starting your BoS with parts you took off and will likely never use.
I'm sure one exists somewhere online, but you might want to make a list of all the styles and designs available for the AR-15 and narrow your preferences using that. For example, if you want a free floated barrel, then that eliminates barrels/uppers with the A2 sight/gas block -- unless you want to remove the sight and replace it with a low profile block. That's just one feature among the many that will need to be considered.
It can be overwhelming if you don't already know which things you want on your new rifle. It's one reason most novices go with a complete rifle for their first. It keeps from buying parts that don't work together, like a barrel with an A2 sight matched up with a free floated hand guard. Or a rifle length hand guard on a carbine length barrel. The list goes on.