I'm going to say Bulbasaur (for FR/LG.) Bulbasaur will help you with the first couple gyms, and will be resistant to the third gym. And by the third gym, you should have some other Pokemon to battle with anyway. So it works out well. Bulbasaur also learns Leech Seed which can be a life saver many times in the game when you run out of medicine.
Competitively, I am going to say Blastoise. It learns Rapid Spin, is bulky, and is Water type. Charizard and Venusaur have more weaknesses. I can't judge movesets as I do not recall generation 3 movesets.