Man... I almost hate to say it, but Naruto. Shikamaru would be my second choice, but as others have pointed out, I think he lacks the proper drive to do the position justice. Naruto has two things going for him right now - he is driven and however stupid he may be, he is usually smart enough to ask questions when he doesn't understand. As others have said, wise advisors can count for a lot.

I also think, looking at their future potential, he has awesome abilites as a leader IF he can learn to harness them. Its already been shown many times in the series that for some strange reason and despite the lonely childhood, these days he is charsimatic and skilled at converting indifferent or neutral people into friends, which can be a huge asset to a ruler. He's demonstrated a huge capacity for hard work, another important trait. And the multi-tasking potential of his massive mastery of shadow clones, both for the purposes of getting things done and for learning new information, is mind-blowing if he can actually harness it. (*has a brief mental picture of a Konoha where a Hokage Naruto clone accompanies every team on every mission...*)