Hahaha! I love ALL Grass-type Pokémon, so all of the starters are my favorites! (I just couldn't choose one, you know?) If I had to choose though, I'd say Bulbasaur or Dodaitose, since they learn more Grass-type moves than the others.
Treecko was the first Grass-type starter I was actually serious about using in the long term, so it's my favourite, almost by default. In fact, I've never used Chikorita in my life.
treeko cuz hes a lizard thingy and so is charizard therfore he must be a charizard lol j/k im just tryin to find out how to make my stuff look cool if ne 1 wants to help plz pm me or w/e