A tie between Garbador and Purugly. Also, I shouldn't ever have looked at the last page. *shudders*
Garbodor is the easy choice... but....
In my opinion:
Worst designed: Klefki; I know t's based off of a Japanese folk myth but I still can't get past it. It has blurred the line between Pokemon and object more than any other in my opinion. I think Klefki is honestly the worst designed Pokemon to date, but it's not my least favorite.
Biggest eye sore: Probopass.... what.... what.... what is that thing?
Creepiest: Banette... it's not enough it looks like something from my nightmares it has a disturbing origin story too. See, Drowzee is creepy but he's cute at the same time so it's okay... same with Litwick and the Gengar line. Banette, on the other hand, I just can't give a pass to.
Overall: There are many bad.... bad...... bad looking pokemon. You'e got Jinx, Stunfisk and half of gen V. To be honest, I don't know if I can single out an ugliest one per say, but there are ones that make me cringe at the mere sight of them.