I've found that the Alliance tends to be made up of more mature, casual player. That is why Ironforge has been my home for years.
Edit: Recently, I've been playing Horde with a friend, and to my surprise I found a guild with limited stupidity. Alliance also seems to own the battlegrounds, so I guess it depends on the realm/battlegroup you belong to more than faction.
Edit: Recently, I've been playing Horde with a friend, and to my surprise I found a guild with limited stupidity. Alliance also seems to own the battlegrounds, so I guess it depends on the realm/battlegroup you belong to more than faction.