It's very difficult to choose one but if I had to pick, it would be Kakashi Hatake. I like the fact that he was taught by the fourth Hokage and eventually becomes Naruto's sensei. Also, he's the man who has copied over a thousand jitsu!
I loved Kakashi Chronicles. It shows how he was with team Minato. He might have appeared to not like Obito at first but we all know he loooveees him! (says he loves him in happy's voice)
Later he becomes an Anbu Black Ops. These were probably some of his hardest days as a shinobi. Thank goodness Lord third Hokage told him to take a break and later making him become a sensei to someone.
Becoming Hokage is no easy thing to accomplish. Like one great man once said, "Becoming Hokage doesn't mean people will acknowledge you, But when the people acknowledge you, you can become Hokage".