I have to go with Kakuzu. He has mais experience than Hidan cause he fought against the first hokage, plus he can use all the elements cause of his multiple hearts. Also, he is mais calm and level headed than Hidan who loses his cool and acts irrationally, plus he's smarter than Hidan. The only real thing Hidan has going for him in the battle is the fact that he is immortal, but that would not matter if Kakuzu cut off Hidan's head and then just sorta left him there to spend eternity staring at the sky like a veggie! lol.
