I'd have to say Squirtle. All three of them have thier advantages in both in-game, and out of game. Charmander is a favorite of a lot of people, partly because most people like fire, partly because it's a versitle pokemon, and partly because its a pokemon based around attack(and sp. attack). Squirtle is nice throughout the entire game, first with Brock, but it works well to win with most of the gym leaders. It has the least weaknesses in the E4, and if you train it a lot, can take out most of the E4 on its own. Bulbasaur has the advantage over the 1st two gym leaders, but has a lot of weaknesses due to it being a grass type. All three have strategies to use in a final team, but there are so many other strategies out there, for me, it is more worth it to use my starter to beat the game as fast as possible so I can start training my real team.