Ichy and Dil win my vote here. Plus some of those weird mammals that appeared in various TV series episodes...they creeped me out. I mean, remember the purple color scheme of that one that helped the Gang out of the Mysterious Beyond that one time? Why purple of all the colors?
I must admit, I'm shocked at how many people think Guido is ugly. I had no idea that was such a common opinion. (Heck, I always thought he was among the cutest LBT characters! He was a big favorite of mine 6-7 years ago.)