Here's one of those situations where I love a Pokemon's preevolutions, but not its final stage. I've always liked Gastly and Haunter, but Gengar just bores me. Plus I like to think that the final evolution of a ghost Pokemon would be its scariest form, but I find Haunter to be a bit more scary looking then Gengar is. I also like Misdreavus. I found the greenish tint in its sprite to be appealing. Unfortunately for me it evolved into a practically all purple Mismagius... how boring. D: It had a nice witch design going on with it too.
So with that I'm going to have to pick Gengar. I still don't care for it much, but compared to the disappoint I got with Mismagius I have to pick it.