I Have now leveled 3 characters to 60 on alliance side and this is my recomendation/experience.
If you are planning to level alone, you should roll horde, it's really a nightmare to level alone after lvl 50 right now... Anywhere you go there are lvl 60 hordes ready to kill you, it''s simply not possible to have a good lvling experience.
But, while I was levling a hunter alone I also leveled a Warrior with a priest friend, and that was a blast. The fact that a single player can't kill you any more eliminates 90% of all ganks and usally u have the edge in random world pvp. Sure u run into ganking squads sometimes but over all it was a realy fun experience.