Started Horde and was horde for quite some time, my first choice was a pure moment of "Haha, I can play a COW??". Then one day I realized that Horde side on my old server sucked, so I went Alliance in order to earn gold for crafted 264 boots. I hadn't been to any Alliance zones before that, and I was struck by the beauty, the feel of zones and cities, Duskwood, the Draenei etc. I just liked it way more than the Horde zones and cities, save for Thunder Bluff. I will always love that place. Also, I did NOT like "the feel" and attitude of players on Horde. This "we're evull"-thing. I just hate it, since a lot of players seem to forget that just because they're behind a big green brute, it doesn't give them the right to grief other players.
Ever since, I've considered Alliance my faction, and Horde the other faction, until MoP hit. Now I have about 50/50 ratio of toons on both sides. I have started playing RACES that I prefer. Goblin, tauren, dwarf, human, worgen, pandaren, gnome, undead, belf. Undead = the race I thought I'd never like. Their lore changed that for me.
So...I'm not with any faction, I'm with the game and I want to experience it to the fullest.