Let me start my reply through the answer to your question which you used to end the post.
It's Pikachu. I've liked Pikachu from my very early age, I like it's voice the most. Then I watched the Pikachu detective movie when I got older and after that I like Mewto a bit.
I liked the graphics of this game.
Well Pikachu is a good choice as a character too, it's the first one you get. My favorite Pokémon is Lucario