what gen?
My favorite is squirtle, but in gen I, red and blue, there is absolutely no doubt that bulbasaur is the best starter by a fucking mile
Advantage against the first three gyms, the three ones that cannot be taken out of order, by the fourth gym you have access to many other routes and you can build a better team, but previously you are kinda screwed against rock if you picked charmander or have to resort to a bellsprout against misty if you chose squirtle. Oh, are you playing red? The only grass type you have access to is oddish? tough shit, misty is going to be difficult.
What makes venusaur scary is two things, first is razor leaf, a STAb attack that, because how fucked up gen I code was, was always a crit, so you had an attack with 165 base power, 95 accuracy and 25pp that ignored stat changes on the opponent. The second thing is the glitch that combined leech seed with toxic. Every time toxic damage grew it did so accounting leech seed, and the damage absorbed by leech seed accounted the one dealt by the toxic.
Gen III? Those games are so easy that which starter to pick matters not
