Bulbasaur>Squirtle>Charmander for the following reasons:
Bulbasaur is clearly the best because of the ingame moveset it can use as the game goes on. My in-game starter, Venasaur (Oakley) knew Growth, Sleep Powder, Leach Seed, and Razor Leaf. Use Sleep Powder. Then while your enemy is immobilized, seed him to sap HP and use Growth as much as you can before the enemy wakes up while his HP dwindles away from Leach Seed. If the enemy wakes up and hits you, leach seed will activate and restore some lost HP. Then sweep away everything with STABBED razor leaf. It’s fun to just let Leach Seed do the work of knocking out the first pokemon while Venasaur is powering up, then you take out the rest of the team too easily. Never fails. I wiped out Lorelei’s whole team with Oakley on my first go at the league and she (Oakley) didn't take a single hit. I powered up while fighting Dewgong and the rest of her pokes went down in a hit. She also beat Bruno easily, and Lance didn't stand much of a chance. I did the same thing to him as I did Lorelei. Plus Venasuar makes the best tank out of the three.
Squirtle is also a good choice because of Blastoise's defenses and it's capability to use Surf and Ice Beam, which will serve you very well during the game and at the pokemon league. Lance and his dragons (Except Gyarados) won't stand a chance against him with Ice Beam. Overall a decent pokemon with plenty of potential.
Charizard is by far the worst starter yet.
Geodude used Rock Throw= 70% damage on Charizard.
Charizard's strongest stats are its Special Attack and Speed, but with his very poor special movepool that excellent Special Stat isn't going to do much for you. All Charizard can use is a fire attack, (which isn't going to help you as much as a growth-using Venasaur or Ice Beaming Blastoise) and Dragon claw, but I highly suggest you don't waste Dragon Claw on this thing. It's not worth it. The only thing Dragon Claw will do for you is help take out Lance on the second go at the league, but Ice Beam will easily do a much better job.
But honestly, Charizard is not worth it. He looks good. That's it. He's nothing but a good-looking sports car with very little power to the engine.