I think that the stance is dictated from the primery power punch you choose to use. If you want to use powerful right hand, you must be as back as possible and with sholders turned less as possible to give you the maximum weight transfer. And if you want to use the left hook you must be squared to be able to slip to the left in order to land it.

From oder hand the stance dictates the deffencive techniques that you are going to use. If you are squared you can forget the sholder roll and if you are sideways you want be able to use the slip to the left.

I think that the problem(who am i to judge, but anyways) of alot of boxers is that they do not transit from the one stance into the oder and they are stuck with one punch. For example Joe Frazier and Gerry Cooney are staying all the time squared and they used only the left hook and in the oder hand are the guys like Sonny Liston. Dont get me wrong here. He has murderous left hook, but he landed it in combos not like leading punch. In order to be complete boxer one must be able to transit from the one into the oder stance. An example for this was young Mike Tyson. Throughout his carrier he stayed with the square stance, but when he wanted to land the right he transited into the position like some one throwing the right from narrow stance.

At the end it for me its about the defence. I have the telling; you can throw as much punches as you wish, but what counts at the end is how many punches have you eaten... So i choosed for me the narrow stance.