I don't like the Dodgers because I was living in Vegas in 1993 and always got into it with Dodgers fans (the Raiders fans of baseball IMO).
I hate the Giants because of their players. Tim Lincecum cemented this for me last year complaining about the humidor and the balls at coors.
I hate the Diamondbacks because it seems like its so easy for them. I predict a Marlins style firesale after the playoffs.