RBY: Krabby. Gets Surf, Cut and Strength, while Fly and especially Flash are uneccessary.
GSC: Poliwag+Chikorita. The thing that sucks is that I always have to evolve one of them for Strength.
RSE: Mudkip+Tropius, Zigzagoon before I get Tropius.
DPPT: I have no real preference here, I don't play them that often. If my starter (of course if I don't plan to use it) is Turtwig or Chimchar, I need a random water pokemon, or alternatively Pelipper for most of the time and a random other one for the Waterfall stuff. If it's Piplup, I will need a Geodude or Machop instead. If I can't enslave my starter, I will get a Bibarel instead.