Pikachu: I know a lot of people don't like Pikachu, but personally I've always liked the concept of the Light Ball. IMO, I'd say it's actually better than Raichu (though neither are incredibly useful).
Doublade: I like Honedge's entire line, but Doublade stands out for me because it can reach an insanely high defense stat with Eviolite.
Haunter: While Gengar is obviously more competitively viable, I just like haunter's design more. Gengar just looks too...fat.
Seadra: I like Seadra's "spikier" look compared to Kingdra; it makes it look more threatening.
