Alright, let's school you boys =3
I jest.
But the reason I say Kenpachi is simply because I feel as though you are not really taking Byakuya's character in the equation.
Yes it's certainly true that he could possess a range advantage, he has the speed necessary for it to be viable. But this is Kuchiki Byakuya! Like he would resort to that. His pride would not allow it.
He is certainly effective at using Kido in battle, and I have no doubt it would have it's uses against Kenpachi but I don't see it being so much as to give him a victory.
He's certainly got more and even better speed feats than Kenpachi. But then I don't see any evidence it would be enough to overwhelm Kenpachi.
If we are to assume Kenpachi is serious about the battle (which is hard for me to picture to be honest. He's wanted to fight Byakuya for as long as we've seen him) then sorry, but I don't see how Byakuya would stand against him swinging with two hands. Even with his Bankai. Ichigo's shikai has shown us the petals can be made useless if they are met with an attack with the necessary force. Two hands is at least as powerful as Ichigo Shikai, as Byakuya's Bankai is to his own shikai.
While it's my opinion based on the scans shown earlier it is insinuated Byakuya's reiryoku is more powerful than Kenpachi's, frankly I think it's wrong. Kenpachi's reiryoku is so strong it manifests visually. Byakuya can only do this with special techniques. In short I put it down to Ganju's poor sense and/or experience of captain level reiatsu.
Result
1) If you're talking about what they can do, Byakuya would win
2) If you're talking about what they would do, Almost impossible to determine (IMO would be dependent on Kenpachi using two hands before it's too late and/or Byakuya realizing the effect that would have)
3) If you're talking about the rules for this thread, Kenpachi takes it.
P.S I actually like Byakuya more. But this thread's rules seem to make it obvious to me than Kenpachi would win.
But of course, this is all just my take on this...