Muman, I understand that Judaism does not agree with Christian theology but just for the record, Christians do not define Jesus as a human being, but rather G-d in human form, so there is not a real analogy between him and David or Moses. The Jewish position on David is that he became such an outstanding and rare tzaddik that he asked G-d to send him the ultimate test of character, that he would be able to prove himself by passing this ultimate test. He was not able to pass that test. I'm not sure what one would call this exercise (pride?), but either way, he did not meet it. He certainly is guilty of sin, as he acknowledged such to the prophet Nathan with no pretense.
I do not think that King David's transgression, as severe as it was, makes him even less of a great or holy man--in fact, I relate to him a lot more knowing that he stumbled badly (and repented of it, and was forgiven) than I would have if he had been sinless or nearly so.
As for Moses' sin, if I understand correctly from church commentaries and what Chaim has said, he lost his temper and cool with the Israelite people he was the shepherd of.