David’s finest moment is not winning battles or not killing Saul. It’s when he is confronted by Nathan for his sin with Bathsheba, and he accepts responsibility and humbles himself before God.
David is different than others kings — both in the past and leaders of today. He does not have the arrogance they have, and he repents.
Although the consequences of David’s sin is far-reaching (one of David’s sons will rape his sister and another will kill his brother and launch a coup against David himself), by admitting he sinned, David is a man after God’s own heart.