But Yahweh said to Samuel, "Don't look on his face, or on the height of his stature; because I have rejected him: for [Yahweh sees] not as man sees; for man looks at the outward appearance, but Yahweh looks at the heart."
Actually, David had a great admiration for Saul. Of course just a young boy, and he was at that hero age, and Saul, big, tall, handsome fellow became sort of a hero in David's eyes. David always respected Saul right to his death and even after his death. David never lost his respect for this man.