I'd pick Itachi. I haven't really seen enough to give any proof, and I think I might've made this argument before, but, out of everyone introduce in the series, Itachi is the most ninja-ish. He has this aura about him, and I have a pretty good idea what gives it. First off, Itachi knows when to run. In his fight against kakashi and the other jounin, he ran to avoid unnecessary complications. In the fight against jiraiya, he ran cuz he didn't wanna risk dying (a very real risk, even if it was possible for him to win) and it was not out of cowardice either. Also, he absolutely destroyed kakashi. If kakashi is supposedly around kabuto's level, and kabuto performed as he did against tsunade, it's not a stretch to say that kakashi is extremely powerful. Final point, Itachi walked in the middle of a village full of ninja who want to kill him, faced off against kakashit, asuma, kurenai, and gai (all at the same time), and then Jiraiya. Itachi did all that, and managed to get away without anyone so much as even coming close to laying a finger on him. Even if no fight was fought to completion, that's quite a feat. These things make itachi look more ninja-ish than any other character to date, and are the reasons I pick him over the others.