Honestly there is no reason for one or the other besides personal preference. Either way you have the exact same classes. I have been horde from day one and will never look back but that is because I just love the fantasy aspect of the "evil" characters. The only difference between the factions is the racial abilities that the races get. If you are looking to play a Shaman for PvP then the Horde orc racials are best. For PvE the dranei and troll racials are good. But then again that is my personal opinion....


ohhh and I would like to add that population really has nothing to do with anything these days. There is very limited world PvP. Everything is determined now by queues for the BG's and Arenas. If you are on the majority side there will be less gankers during the leveling process Just food for thought....