Sasuke, because he is a whiny brat who thinks he has to tear down the world just because his life sucks. He gets handed power on a silver platter that he doesn't deserve, and he doesn't have the maturity to use it properly. He wants to tear down his village because someone who is now dead gave his big brother a terrible choice to make, that resulted in Sasuke's life being spared. And even when his brother's wishes are clear, he still goes against them and decides to avenge his brother (when Itachi really doesn't want to be avenged). So Itachi turns to Naruto, who reminds him of his best friend, in order to save everyone.
Sasuke has potential, but uses it all wrong, which is why even his brother has more faith in Naruto than in him. He made his bed and he doesn't want to sleep in it. He refuses to see past his own pain, he is conceited and thinks that he is the center of the universe.
That is why I find Sasuke to be the most annoying character. I preferred him during the chuunin exams and before he saw his brother again.
