I'm about to finish a Catch 'em All run of the gen and I couldn't resist kicking off this argument again. Lets start with the basics.

>Pikachu and Charmander are simply wrong. If you want to argue in favour of either of them, you're going to have to do a really good job before you'll even be taken seriously
>'mons that come early but aren't starters don't count, no Nidorans or Mankeys.
>all of these 'mons are competitively irrelevant, no playing that card

Anyway, here's how I see it:
Bulbasaur's pros:
>it's typing lets you ignore almost every part or fully Poison type Pokemon, which is a fucktonne of Pokemon
>it's (very late game) access to Sleep Powder makes it great for catching Pokemon. Leach Seed, which comes extremely early, is also good for this job
>can humiliate the Pewter Gym
>will humiliate the Cerulean and Viridian gyms
>not bothered by the Vermilion, Celadon, or Fuchsia gyms
>Razor Leaf is great, but comes late
>difficult to replace

Bulbasaur's cons:
>Leach Seed is offensively shit, and Vine Whip often comes a level too late for you to use it to humiliate the first gym
>even when you have Vine Whip, it's only got 10 PP, making it a pretty bad candidate for the job of powering through caves like Mt. Moon
>speaking of caves, it's got a 4x weakness to bug, meaning that Zubat's Leach Life can seriously damage it
>will have trouble with most of the E4
>humiliated by Saffron and Cinnabar gyms
>HMs/TMs can't do much for it, even Mega Drain has worryingly low PP

cont