Squirtle. It can defeat the first gym leader easily. Also, for defeating your rival you can catch a bird pokemon at the beginning and train him high to beat the grass type. For the other two you'd need a Electric/grass type or Water type to beat their rival's main pokemon, and they're not available at the beginning.
I would choose Bulbasaur. I like annoying moves like Leech Seed, Toxix, Sleep Powder and the Synthesis, Sunny Day, Solar Beam combination. No charging for Solar Beam afyer Sunny Day, maximum effect on Synthesis and maximum power on Solar Beam.
I'd choose a Charmander. I love lizards and it might be more diffucult for some of the earlier parts of the game..But I think it becomes totally worth it later on.