My least favorite is probably the Ghostly, it's just really plain and meh. Even the redrawn colors are boring.

Started wondering about the answer and realized how damn picky I am... Experiments are all ugh, except Chibi peacock. And from regular pets I dislike all bug type, all dino type, both robotic ones, Ghostly, Harvester and Warador as looking too human-like... phew. Good thing that still leaves so many of them I adore ^^