You asked about an "accurate" gun. That means different things to many people.
I will skip a bunch of typing and just say this; I would use a White Oak Armament upper in whatever configuration best suited my needs and tastes. I would put it on a good quality lower that had a decent trigger. A good Colt, BCM, whatever. That matters a lot less, as long as it is quality, and assembled by someone who knows what they are doing.
https://www.whiteoakarmament.com/I have used White Oak barrels and uppers in more than 2 dozen builds for guys and all shot very well. Usually using MK262 (77 grain Sierra Matchking), but that was what was available for them at the time and location.
Bottom line is that it is extremely easy to simply put a WOA upper on a good lower and be done.
I've got 1 WOA barrel on an SPR build I did, 18" fluted SPR profile. It's shooting very well.
5rds of Sierra 77 grn OTM at 100:
3rds of 77 OTM at 307yds on my turkey swinger head, quit when the bolt head broke off:
I've taken it out to 600 yds and it holds with our .223 bolt guns.
To the OP, it all comes down to task/purpose.. accuracy requirements and budget.
The good news is whatever you get now can be easily modified later if it doesn't match your needs. But as the other guys mentioned, there's a chit load of difference between a defensive carbine set up and a precision rig IE; barrel length, profile, trigger, optic, trigger etc.