I'd go with Kakuzu. The man is one of the few people in the series that is legitimately powerful. He got stronger through training and survival in the Ninja world. He had experience, a powerful forbidden technique and he was shrewd and logical (Kishimoto making him stupid enough to fall for a Shadow Clone, Not outright snapping Chouji and Ino's necks and letting Shikamaru take Hidan away aside). Plus, he was funny when he went on his rampages and argued with Hidan. I also liked how he viewed Death....he just accepted it as an inevitability.
Tie between Naruto and Shisui. I love how selfless and giving they are despite the world crumbling around them. That kind of courage and bravery is so rare and I really admire it.