Treecko, for the reasons below:
I like Grovyle's design, especially the leaves on its arms as well as the large leaf on its head.
Sceptile has an amazing 120 Base Speed, allowing it to outspeed quite a lot of pokémon. It also has an amzing 105 Base Special Attack.
My favorite one is definitely Bulbasaur. The lamest one EVER is Snivy. It's just a worse Chikorita with worse stats on everything except Speed, I should've picked Oshawott instead. Bulbasaur is sooo AWESOME!!!