With our inevitably human-centred-and-biased eyes, I believe that we can easily say that:
the Alliance are "normal" to be picked as "good guys."
and the Horde are for those who want "cooler and wild" antagonistic roles.
because of the above reasons, I wanted to pick a Horde race in vanilla WoW. Although my main race was NE in WC3..
Even the colour schemes and variations of Horde races are very attractive to me, especially when I compare them to relatively more mundane Alliance races, despite the lores.
-of course, only until Worgen came out and brought a cataclysm to my mind <3-
However I never raised any Horde characters cos I wanted to fight against those bad-ass Horde players and that seemed even more cooler than being one of them, you know what I mean?
I knew the Horde will be full of players who are more competitive and aggressive in pvp, and probably will be full of haters who will assume that I'm for sure one of those ordinaries that they want to face-stomp.
Well, it's not been easy to be a pvp-lover and an Alliance player at the same time,
But it still gives me a bigger satisfaction when I defeat those who are considered better in pvp than my faction; the Horde feels like elite forces that are outnumbered but skilled. (although population ratio are pretty equal now)
Anyone else is playing Alliance for this kind of reason? :P