Both scholars and practitioners over the years have failed to produce a clear profile of the ideal leader. Which approach to leadership you think is ideal?

I believe there's more than one prong in any approach to leadership but if overall I was asked to sum it up, I'd say that having integrity and a 'greater-good' approach works a treat. These are indeed rare qualities as the leader should be conscientious, be a clear, concise communicator having already achieved personal authenticity while being caring and compassionate, wherever possible. It is always possible :) 

There isn't one.  It depends on the circumstances and the character of the leader. 

Good leaders are flexible, and adapt to the situation.