For bug it should be BW2, since it adds Heracross and you can get Volcarona before the league, but I'm not that sure because you're somewhat fucked if you want Escavalier and Accelgor.

I think HGSS have a great variety of water pokemon, and Pt is probably the best for ground types (Torterra, Garchomp, Gastrodon, Gliscor, catchable Steelix, etc).

I'm not sure about the rest.
Discuss.