This is a battle that will never end i mean.. Hidan is immortal, so poison would not work. Orochimaru is kind of immortal also, his abillity to regenerate is awesome. Even if i consider Orochimary stronger than Hidan i can't see a way for Orochimaru to kill Hidan(Edo Tensei is not allowed). I know all will vote on Orochimaru but i will not because i can't see him do a devastating attack that will kill Hidan, nor will Hidan have an attack against Orochimaru that will work. I'd say this is the battle that never will end.