Madara, that guy still hasn't gone down, fighting against five kages so ...
And Sasuke. I know most people won't believe that, because they are bent on believing that Sasuke is weaker, but it's actually logical.
Naruto still considers him as a best friend. No matter what Sasuke does to him, shoving a Chidori through his chest, threatening to kill his friends, insulting him ... No matter what he does, Naruto still considers him as his best friend.
Plus it isn't in Naruto's nature to want to kill (except for the people who really piss him off by threatening his friends like Deidara and Tobi). So when it comes down to those two in a fight, I can honestly see Naruto holding back just because he doesn't want to kill Sasuke. Plus Sasuke isn't weak at all. If he wants to kill someone, he gives everything he has in him. So if he wants to kill Naruto, well, then Naruto is in some serious shit. Because contrarily to him, Sasuke won't hesitate to kill him.