Between Darkrai or Lucario Darkrai has a Calm, Sneaky, and Cold Character, while Lucario has a Strong, Loyal, and Brave Character, i really like those. Also, Both of them have awesome designs, and are good in competitive battling, both posses a huge variety of movepool to use.
first favorite is bulba (its so fcking cute), second is gyara (op sweeper in competitive), third is probably going to have to be gengar (hypnosis + dream eater/hex combo).