I would give it to Danzo in both.
I can't see Shizune being helpful to Tsunade in any way other than healing, and even then... But other than that Izanagi will give him the overall advantage, since any attack he inflicts is fatal (And she has no real defence to block them, unlike Sasuke), and he is easily more versatile and skilled in combat than her. Not to mention he was able to track and take down multiple ANBU level assassins without the use of Izanagi (I am starting to think that the ANBU are not as good as they are made out to be). Also Baku would give him another advantage since Tsunade would have no way of putting it down. And he has Kotoamatsukami just to top it all off.
As far as her Byakugou goes, Im not all that impressed with it to be honest, it seems more like a plot device than anything just to keep her alive. Could she even heal from a fatal attack?
And I can't really see either doing much with prep.
Also I feel the need to ask, would Fuu and Torune be in the second round with Danzo? I cant see there being much difference, but, you never know.