I've found that some of the nicer AR factory barrels can be surprisingly impressive. They offer good accuracy and consistent groupings and I never felt the urge to replace them. The same goes for a couple of bolt-action rifles I've had since they were so well-tuned right from the factory that swapping in an aftermarket barrel would have been more about personal preference than any real need for improvement. It doesn’t happen all the time but when you find a barrel that just meshes perfectly with your ammo and shooting style, it’s tough to justify changing it up.