Who is the most valuable Celtic?

Since the Big Three came together, there was always a hot debate as to who was the most valuable out of the three. Many people view Doc Rivers as the most valuable Celtic. When the question of who the best coach in the game is asked, Rivers' name is always in the conversation. His ability to be blunt with his players, but also caring for them like they were his own sons make Rivers a popular head coach. With the departure of Ray Allen, and the emergence of Rajon Rondo, mainstays Paul Pierce and Kevin Garnett continuing to thrive, and a head coach with a tremendous reputation, the question remains...Who is the most valuable Celtic?