What are the best Pokémon to choose as the player/partner?

IiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIi

Chespin seems to be commonly regarded as the best. It starts out with Pin Missile, which hits multiple times in one turn, even from a distance! This is fantastic, especially after the move levels up a bit. Chespin also starts with Defense Curl, which makes Rollout (learned at level 8) crazy strong.
Charmander is also amazing, starting with Dragon Rage, which deals a fixed 30 damage (powerful for the first chunk of the game).
Both of these guys totally tear through enemies! Most other choices are solid, too, though Chikorita, Snivy, and Froakie seem to be the toughest to use.
IiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIiIi