grass types are easy to catch where fire type are rare, plus Charizard has better typing, and in firered he gets metal claw at level 13 to held fight brock.
however Blastiose's line has been statistically proven to be the best option for the game.
first gym good (metal claw)
second gym bad (but lots of grass types in the area that are easy to catch)
third gym neutral (use but magnimite is part steel)
forth gym Great
fifth gym neutral ( but unlike bulbasaur no weakness)
sixth gym neutral ( bulbasaur is immune to poison...)
seventh gym neutral (but not weak, and you have lapras)
eighth gym immune ( its a charizrd now)