Cyborg Superman, definitely. At least through the end of "The Trial of Superman", anyway, when they threw him into a black hole. He kinda went a little "out there", after that, although his role in the Sinestro Corps War almost made up for his lamer appearances.
He had the advantage of his Kryptonian tech, plus the DNA of Clark and all the benefits that go with that. Truly an "evil twin", so to speak, of the Man of Steel. Just loved him, and I hope they find a way to bring him back in the New52 (as a Superman villian...if it's just as a foil to Green Lantern, they can keep him).
Oh, and the guy who mentioned Word Bringer? Awesomesauce! One of my favorite all-time issues is during Exile, when Clark lands on that alien planet...and the horror and disgust on his face when he realizes that the Word Bringer has been there. Nice pick.