Bulbasaur, Charmander or Squirtle for a first FireRed run?

Bulbasaur if you want the easy start. It's strong against both Brock and Misty, so the first two gyms are a breeze. Charmander is the hard mode pick early on, those two gyms are rough, but Charizard is great later. Squirtle sits in the middle. None of them make the game unbeatable, so just take whichever one you like the look of.