My least favorite Pokémon are Blaziken, Manectric, Lucario, Gyarados, and Regice. I think Blaziken is silly because it's a flaming chicken, which is like a chicken cooking itself. I don't know how Game Freak made that look cool. Since most people I know choose the Fire starter, I feel that the Water and Grass starters are overshadowed and tend to like them better than the Fire starter in general.
Manectric and Lucario aren't my favorite because I feel that they were designed to look cool. As soon as I saw them I knew everyone would have one. I don't like Gyarados that much because I can't unsee its Gen 3 sprite. Regice has one of the most intimidating cries in the game alongside Giratina, looks a lot bulkier and less like a human and more like a killing machine than the other two Regis. The suspenseful theme music didn't help
What are yours?