You can really level with anything. I'm Prot specced.
The best for leveling overall I would say is Arms but it's mostly based on how you play and how well you know the stance you are in. Basically it's:
Arms - PVE - Two-Handed, Slow, Big Damage Weps
Fury - PVP - Dual Weild, Fast Weps
Prot - Tanking - Shield and One Handed Weapon
But again, you can own in ANY stance with ANY talent tree as long as you are geared properly and know what you are doing.

actually arms is mainly for pvp and fury is mainly for pve. u NEVER see an arms specced warrior in a raid, what u do see is fury warriors.