From a competitive standpoint, I've always cried in agony whenever I've seen a Breloom on the opponent's team.
Design-wise, I can't say I outright hate any design, but I guess the closest would be Zoroark. Probably a bit odd coming from someone who's made it obvious that they love Zorua, but it's an illusionist fox kit that I found outright adorable (IMO) whose design is very different from Riolu's. Seeing its evolution being... that Lucario-esque thing just doesn't settle with me well. :/ I personally don't "hate" Zoroark as much as I "wish they took a different approach with its design", but it's the closest I've gotten to hating a design, you could say. <.<
3DS: 3566-1678-7442 (Mid*nite) Official Zorua of the Pokemon X / Y boards.