I think it was Charmander. At least I have some distant memories of getting pwned by Brock every time I attempted to fight his Rock-type Pokémon, and you don't have that with Squirtle or Bulbasaur...
Incidentally, my first Pokémon game was Red, and it was fully translated into Spanish. Playing an RPG in a language you only know a few keywords of (Si, No, Gracias, nowadays I know a bit more but still not enough) is not a great way to learn anything, but last time I checked out Red (years ago, only checking it after even more years of not playing it) the character actually was in that one scary town (Lavender Town?), so somehow I must have gotten through the first two gyms despite having not the slightest clue what all the characters are saying...