While they are supposed to be - legally - a total of 16 inches (per ATF definition) most civilian barrels made are still 16" without the flash hider or similar device.
So often the go way longer than needed legally.
Me being extremely passionate about US military AR15s (not interested much in any other) I never truly liked the 16" barrels with their profiles.
Mind you, this is completely just aesthetics. So it's not at all (for me) a functional aspect; it's only a hobby for me and so it'll stay.
Mostly, I like my rifles for how they look and I set them up mostly in that regard.
So this is almost exclusively a looks related thing for me.
With that clear for you,
Specialized Armament is an Arizona based company operating for the past 25 years. I am sure several on this board know it. They are considered the Colt custom shop in the country; even Colt itself considers them highly.
When I learned of how they shape civilian Colt barrels to make them look like the military ones, I was sold. So much that, I purchased two 6920 Colt Uppers and had them do the work.
More at the link and a couple pictures of the final result.
Specialized Armament Civilian Legal 14.5 'looking' barrels.