I am extraordinarily partial to Dragalge, and delighted that there is even a Pokémon in existence based on the weedy sea dragon. Its splendid typing is a cherry on top! Maybe even two cherries.
As for my least favorite, that honor goes to Binacle, no doubt. I can't even appreciate the concept. It is some kind of awkward, petulant-looking arthropod that is also a hand. Er, hands. Really, everything about it is unsavory, from its palette to its faces. Even its X Pokédex entry is especially ridiculous, and considering the absurdity one regularly encounters in the Pokédex, that is really something:
"Two Binacle live together on one rock. When they fight, one of them will move to a different rock."
Not only is this utterly underwhelming, I am also having a difficult time reconciling the bizarre contradiction.
Taking its evolution into account, as well, it just ends up somewhere between silly and nightmarish. I would simply rather have nothing to do with this aquatic abomination and its angry puffy palm-cheeks!