I used to at least have a Dragon type in my team (wich isn't the case in Leaf Green and White 2), but I always try to get a Dragon type in my team.
But I always, always, want a Water type in my team. I refuse to use any type else (such as Stoutland or Tauros) to get Surf. If my starter isn't the Water type, I always go catch one. Even there, sometimes I catch one with a Water type starter (Blastoise and Dewgong in Leaf Green). Same goes for a Flying type to get Fly.