But before we could do any stat training, charizard's defense kinda sucks ass and a having a strong/supportive grass type is better than having some weaker grass type that hardly does anything for you (speaking especially in the context of gen 1 when there weren't many strong grass choices), and blastoise is a goddamn powerhouse with good defense and is good for strong and useful moves from lots of different types. In the gens especially before stat training, I would pick blastoise first, venasaur second, and charizard third. I'm not saying that it doesn't have its uses, but when used well the others can bring a better balance to your team. I usually don't waste my starter on a fire type; there are usually pretty good ones you can find along your journey that get the fire job done anyways.
Always start with the water types