My first favorite Pokemon was Mew (back in the old 151), but then the 256 Pokemon came out, so I had two new favorites: Celebi and Lugia.
Now, with all the... well... weird Pokemons*, Deoxys (SpEeD Forme) was added to the favorites.
So, my favorites are Mew (shiny, 1st place), Lugia (normal, 2nd...