Nightmare hands down, he has that killer fast move that knocks the opponent away to give you some breathing room, plus some massive smashes with the sword.
Second is Mitsurugi. He's a samurai, katana, japanese and is the most complex character in the game.
Last one is the special guy in Soul Calibur 4, namely, The Apprentice. Seriously, the guy has so many combos it's not even funny. For example, you could do one punch, then take that like 5 different ways!