Madara has done **** all, so it's not him.
Obito has been fighting Kakashi a lot recently, but if he survives he will improve the manga with his evilness. ONLY if he stops begging for a talk no jutsu.
Orochimaru we have yet to see if he is evil, and if he is. . It would probably be in some next arc labeled "Juubi's final form" or whatever.
Sasuke has the chance to flip his lid and kill everything to protect Konoha/
We. . Don't really have one? The closest person we have is Obito.