Alliance is usually more casual players, you know, mostly 14-17 year olds, just playing this in their spare time. Horde is more of the 21+, read all of the books, knows how to make a private server, plays for over 24 hours on end eating doritos and drinking mountain dew from a 2 liter bottle than peeing into said bottle so they don't need to get up, openly devoting their exsistence to the game kind of person. Of course, either way it's just a stereotype. The real question is what race you like most. You want to play an undead? Don't let the enormous NEEEEEEERD population keep you away. There are plenty of casual players there too. Just not as many.