I would pick a Pokémon which would evolve twice, and the first at an early stage. Nevertheless, Pokémon (other than the real starters) like that are impossible to find. Eevee would be the best choice then, except you wouldn't get stones that early, or you would want it to be Espeon or Umbreon (which then requires happiness). But suppose, you managed to hobble up to Celadon with Eevee then xD. Also, other than Eevee, I'd really love Mudkip (it's a generic starter already, how lucky!) to take. Very nice little thing, also helpful 'cause it evolves early (like other starters, except this guy is my fav). Also, an ideal starter would be a one who looks normal, and can cross any terrain (in other words, have legs). He shouldn't be terrifying and should be small and naive like you. Not some hurly burly Rhyhorn, or some spooky Gastly. Not that I hate them, i'm just saying why they aren't starter-friendly.