I'm tied between Garbodor or Simisear. Thing is.... just ugly. Bad proportions (a monkey with a beer gut?), only has speed on its side, looks like it's missing half a brain... at least Garbodor looks like it's aware of what's going on around it.
You know what, I've decided, it's Simisear. I hate Garbodor (and for those haters, Druddigon, too), but Simisear is the worst.
And, this may not be the right post, but... Dragon Eeveelution? Ghost Eeveelution? Unova seems to have sprouted a lot more Dragon-types than other regions, even if they got bad and ugly ones, so I'm surprised they didn't muck up a random new Eeveelution.