I would pick the Kanto starters—Bulbasaur, Charmander, and Squirtle. I love all three, because they seem to be quite cute to me. :) They're extremely well-designed. If I had to pick one though, then I would have to go with Squirtle. It's a small, soft, squishy, happy-go-lucky turtle. Is there anything that you shouldn't like about it? xD This Pokémon should be able to have your mood lit up as soon you it touches you, haha. Plus, when it finally evolves into a Blastoise, it gets two huge cannons stuck onto its back. It utilizes these cannons to blast a variety of attacks, such as Water Pulse, Hydro Cannon, Flash Cannon, and Hydro Pump. How awesome does that sound? When it comes to competitive battling, Blastoise isn't that bad of a Pokémon either. It's got great defensive stats, which allows you to use it as a wall pretty easily.
My second favorite of the Kanto starters would have to be Charmander. The flame on its tail indicates how much strength it has, which I find to be really interesting. If the flame is shining brightly, it means that the Pokémon has enough energy in its body and is ready to do almost anything. If the flame is a little dull though, then that means Charmander is feeling weak and needs to be healed.