When we compare this to Michelangelo's statue, you can understand better why Donatello's work is not idealized. He is portrayed as a young boy, while Michelangelo has depicted the idealized perfected form of David, at a young age, but still a man. Donatello's pre-pubescent statue is not yet grown into himself, and Michelangelo's David is at his height of glory, age, wisdom, and physical status.
Bernini has taken his David to an entirely new level --he has depicted David in the midst of throwing the rock at Goliath. You could almost compare the progression of this character's portrayal in a similar way to the progression of the art of the ancient Greeks (early classical, high classical, hellenistic). Bernini's David is exaggerated in mid-movement, with dramatic expression.
So to settle the argument of what it means to be idealized, Michelangelo's statue wins the title. Donatello has begun the journey, and Michelangelo takes on the height of it, while Bernini develops the pose, movement and rendering of the actual story itself as opposed to a representation OF the story.