Gallade is my all-time fave! He can learn some pretty useful moves, his design is epic, Fighting and Psychic are my favourite types (along with Ghost, Dark and Grass)
I also really like Lucario, Weavile, Staraptor, Kyogre and Chikorita
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.