You are all casuals with filthy casual reasoning.

Charmander/Charmeleon/Charizard have the highest Speed and Special, and therefore, the highest DPS in Generation I. It's the best for players who don't know what they're doing, because even in Generation I, Charmander can defeat Brock, simply because Onix's Special stat is so low, so Ember can kill it in five turns at level 9. Charmander only struggles with Misty, so the real question is, why haven't you caught a Pikachu (also an OP Pokemon)?

Squirtle is the best for non-glitched any% speedruns. This is because of its typing, which allows it to survive the Misty encounter with ease, which is something the Nidoking runners struggle with and where most Red/Blue speedruns die. Squirtle can learn Mega Punch and Mega Kick, giving it access to some very high base power moves. Even in Nidoking runs, Squirtle is the starter of choice (because it makes cutscenes go faster).

Bulbasaur is currently the best starter for catch-'em-all 100% speedruns. Charmander, Squirtle, and some other version Pokemon are easier/more strategic to generate with a fully optimized name for the Old Man glitch. It's the fastest overall until you can generate a level 100 Gengar in Mt. Moon, so Bulbasaur's traditional weaknesses (typing, poor moveset) don't show.