I’m going to do my best to make this article as un-biased as possible, because I want for all players to choose the faction they wish for based on their own opinions, not on mine. But first things first, when it comes to choosing either Alliance or Horde, there are definitely a few things to take into consideration first.
Do first appearances look good to you for either of the two factions? Do you like the Horde because of their brutal appearing orcs, or the Alliance because of their mystical looking draenei? There are going to be obvious first impressions of both the Horde and of the Alliance, and you’re going to automatically want to be the faction which you think appears more desirable.
Figure out what class you want to be. This may be hard, because if you’re choosing your faction you’re probably new to WoW and therefore don’t have any clue what class you should be. I recommend just choosing a race you really like and picking a class based on this.
Player Versus Player Status
Here’s where the fun really starts. I would say that on most realms, the Horde seems to have a general advantage in player versus player, simply because they typically have a few more players than the Alliance does. However, this does not mean to go Horde just because they have it the easiest. As Horde, it means you’re on the team with more players. Therefore, you’re going to have a harder time finding other Allies to attack. If you’re Alliance, you’re going to be up against a larger force, and therefore running into Horde players much more often is a given. If you’re really interested in hot PvP action, regardless of the outcome, play Alliance (in most cases, may vary by realm). If you just want to play it safe, go Horde. Again, this is assuming that most realms are like the several realms that I have played on, and the vast majoritty of them are.
Of course if you’re a new player, you won’t know exactly what to look for in the cities, but I would say that your faction’s cities is often an important part of choosing your faction. The Horde tends to have more brutal, or dark types of facilities. Orgrimmar (the main city) is in a desert type landscape with all buildings appearing to be small huts and what not. The bank is made of stone, and overall the city fits the faction. The Alliance main town, Stormwind is more like you would see in the movies; A castle surrounded by a beautiful landscape, where all of the buildings are more advanced looking in the role playing world.