The best written characters, you mean?
Jiraiya is a top notch written dude. He's a pervert and a funny guy, but he knows when he needs to be serious and buckle down. He's also an honorable man and a great father-figure.
Tsunade is pretty good as well. She has had phobia's and family deaths in her past, alcohol problems. ETC, but she has currently managed to over come them, now if only she could work on gambling.
Zabuza is an intense character, it's ashame he never stuck around for a bit longer. He's ruthless and evil, no denying that. But at the same time he shows a softer side and hidden love for Haku. Willing to jump into an armed mob after being considerably weakened from Kakashi; Just to make the one who dishonored Haku in death pay.
Kabuto has one of the best written characters around. He has always been an interesting character. In Part 1, he interacted with nearly everyone and has shown to be both intelligent and deadly. Several moments in the manga we're given clues that he may betray Orochimaru, making us raise our eyes at him.
But in the end, it turned out he idolized him more than anything else. And, during recent Arcs, his goal is not something to out of the norm. He's had a terrible younger life and just wants to find his place in the world.
Kisame's a great one. While I am biased to him, he's a fantastically written character. He's dark, evil, and a loyal soldier. Willing to kill his own comrades for a mission, sacrifice his life to keep intel, all for a dream of his.
He's not overly boastful will listen to Itachi's wisdom, and even formed some type of bond with him. Not to mention his attitude is slightly funny; Especially when he is talking with Gai.
