On my main file, it's gotta be Ocelot (Samurott). Once he gets a swords dance set up, he will do some major damage. Zinaida (Luxray) has her ace moments, especially when she gets burnt or poisoned, because guts is a great ability.
As for my mono dark file, it's either Zabuza (Greninja) or Deva (Honchkrow). Occasionally Noxron (Malamar) has his moments of being my ace. He was amazing against Charlotte. contrary + superpower x 4 = win.