Actually, the most played schools are in this order, Fire, Storm, Death, Myth, Life, Ice, Balance. Balance and ice are constantly shifting, but ya, there ya go. The best in my opinoin is death.
I see a large amount of fire school players, more than I see of either storm or death. So in game play I think I'd say fire is the school I see the most, in pvp storm, fire, death, balance, and life seem to be played a lot and ice isn't that uncommon either. So in general, about every school is played quite a lot, and many people have multiple characters of the various schools.