It'd have to be Crobat for me. I don't know what it is exactly but I have hunch I can explain why. Pretty much nobody likes Zubat. They harrass the player in every single Pokemon entry and their always associated with generic filler for Team Whatever. Their like the official mook of Pokemon. Golbat isn't much better either, I personally like him even less than Zubat. He has an obnoxious appearance and sometimes still fills the ranks of Team whatever. But then its all ok in the end because after going through the puberty that is Golbat you get Crobat, the coolest bat pokemon ever and who's even pretty decent to use. Its evolution thematically makes sense as well, it only evolves after you befriend it enough, which is why the evil teams will only be stuck with its middling pre-evolutions while those who stick with it get the awesome terror that is Crobat.
