Any water-type pokemon that knows surf is a winner in my book! I would say Samurott, and especially if I get a Samurottite when I transfer him to Pokemon X/Y/OR/AS! I always liked Oshawott in the anime, and when I got Pokemon Black Version, I chose him as my starter. Once he evolved into Dewott, he started wrecking face with his Razor Shell, but then... Samurott. Samurott was one of the strongest pokemon I have ever seen, and when I got HM Surf, hoo boy, I started REALLY wrecking everything that was sent my way. My Samurott and my Sawk are my MVPs. Cryogonal? Sawk, Karate Chop! Serperior? Sawk, Karate Chop! Emboar? Samurott, Surf! Unfezant? Samutott, Surf! Plus, you can use Surf over water, so it's a double-win!