1. Torkoal. It's fiery, it's a turtle, what's not to love?
2. Squirtle. It's a turtle, similar to Torkoal, but it doesn't have the base stats to function without evolving, and I don't like its evolutions nearly as much.
3. Mewtwo. Still has the highest Sp. Att in the game barring Attack Deoxys.
4. Giratina (especially Origin Forme). It's like... the grim reaper of Pokemon. It reeks of death and destruction, which is refreshing in this particular series.
5. Porygon-Z. This piece of poultry has some nice stats, plus I just like the overall look of it.