I'm going with Kiba. People really underestimate his speed. Sakura has no chance in hell of evading his attacks. Two headed and three headed wolf are overkill. The only way that Kiba will lose is if Sakura summons Katsuyu, but think about it. Why in the fawk would she summon Katsuyu in the middle of a 1 vs 1 battle. Sakura only summons Katsuyu when she needs to heal a bunch of people.
It's funny how Sakura can only win with that irrelevant slug that can only shoot acid from it's mouth which Kiba can easily dodge. Part one feats, Kiba was owning Naruto in speed, so Sakura has no way to hit Kiba with her slow one directional assaults.
Sakura is basically a slow boxer with much strength. Just like Goku said, "what is the point of all this strength if I can't hit anyone"? Tsunade and Sakura are good examples of this. They can swing their fists all they want to, but when it comes down to it they are slow as shit when it comes to attacking speed.
All in all, Kiba wins medium difficulty. It's high difficulty depending on the slug though I don't think it will be that relevant because Kiba also has a partner to fight with - Akamaru.