<poll> Who is stronger Kenpachi Zaraki Byakuya Kuchiki They're about the same </poll>
Well, there has never been a full battle with them, where one has acually won. But its probably Byakuya.
Undetermined: While Byakuya is said to be the stongest on several occasions, they are actually referring to his zanpakuto. Zaraki Kenpachi, with his name, he actually holds the title of "stongest shinigami," as his name is actually a title, because he didn't have a last name before he gained the title "Kenpachi." ... that said, Head Captain Yamamoto is actually the stongest, in strength, reitsu and zanpakuto, though your question didn't include him.