Pain would be my first choice, but I'm going to use my nomination to expand the number of nominees. As such I'm going to nominate Yamato. He's not the most powerful fighter out there, but he's a great secondary character that constantly brings humour to the manga whenever he's active in the plot. Too bad he got abducted to power up the Zetsu army, I would have enjoyed it if he was present at Naruto's current battle.
I support Yamato as well.
Poor guy can't get no break, you just gotta love him.
Naruto-kun...I've always...always been chasing after you. Even...now. But... once this war ends, I'm going to stop once and for all.
Next time, I'll be next to you, holding your hand...walking with you! Wait for me!!
Is it allowed to nominate Shisui? It's a little bit irritating, since we never saw him alive/in action. And the second point is that his name was mentioned in Part 1, but only in Part 2 we got the information what kind of a shinobi he was.