Bulbasaur. It's actually the only dual type basic starter which is pretty cool, having grass/poison. Leech seed proved to be very helpful in difficult situations, and acted as an emergency health item, if you're running out of potions. A combination of sleep powder, and leech seed grants free turns of healing, which you would mostly need during your kanto quest.
//offtopic: My interest in bulbasaur was more of during a battle in a different generation (competitive), and when I went back to play the original rby, only then did it pique my interest that bulbasaur was indeed my starter of choice.
it has advantages on the first gyms as well, so it wouldn't be difficult to train it in anticipation of the tougher challenges.