Since I know which Naruto is being used now...
Using Kyuubi mode is tempting. He can fly through most of the beginning fighters with relative ease, except maybe Neji and Lee. However, he would likely stop at Choji, who would not be so easily one shotted. Remember, Naruto doesn't exactly have full mastery over the speed of this new form(from what I've seen anyway) and could very well injure himself along with his opponents. Also the longer he stays in it, the more perilous it would be to him. If he gets past Choji, and there is a fair chance he will, Guy will end him. So Kyuubi Mode is worthless. It doesn't capitalize on the prep time and leaves him without the ability to use clones. So he'll need that as a trump card.
So that leaves him with Sage Mode. I like the idea of sending clones off to gather chakra while speed blitzing as far as he can with initial Sage Mode....but Neji will literally see through this. The area is smallish and with the ability to see all of the arena, he could find the clones and destroy them. His kaiten can protect him until then. Naruto would have to be clever to get passed Neji. RS would do it but that would be suicide.
Which takes him to Lee and Shikamaru, who will wear down what little Sage Mode time Naruto has left. If he makes it through, Choji can stop him. If at this time he goes into Kyuubi Mode, he might get past him. But it will not get him through Morning Peacock/Afternoon Tiger.
So he probably loses. Yay I guess.