Having played both games for extensive periods of time, I would say that the AH population is much older and much more male. WoW's gender balance, on the server I play on, is about 5-6 guys per lady in my experience. I am not sure what AH's ratio is, but 500-600 guys per lady might be roughly in the ball park.
WoW is much easier to hang out with RL friends as I haven't had much luck at all getting them to try, or stick with, AH. WoW is a better co-op against the program game.
AH is a much better PvP game though. AH's combat is also much more complex and more prone to tactics rather than reaction speed. Blizzard had tried several times to reduce the pace of their PvP, but it remains a huge problem there.
