Well it depends alot on if you ask if "longer is better." Nowadays on a standard hunting rifle barrels are 22 inches long. But For tactical and match shooting that is within oh probably not much longer than 600 yards (I'm not for sure though about how long away) a short, heavy barrel is better. That is because of the rigidit of such a barrel. A short barrel doesn't "whip" back from recoil and a heavy barrel is almost always more accurate than a smaller diameter one.
Of course the match shooting out to 1,000 yards and so on you'll need all the velocity you can get, so they opt for probably a longer barrel. And varmint hunters also have slightly longer barrels some times.
But this is just what I have read about and observed, so correct me if I'm wrong.