To me, the candidates would seem to be Shane, Hohmann, Orcullo, Feijen and Vann Corteza. Ko Pin Yi did have a huge win at the Japan Open, but, to me, he didn't score enough big wins to merit consideration.
Here's the case for each:
Shane Van Boening
Won the US Open 8 ball and the US Open 9-ball and the Players Championship.
Thorsten Hohmann
Won the World 9-ball Championship and the Dragon 14.1 event, second at the Players Championship.
Niels Feijen
Won the World Pool Masters, 2nd at the World Cup of Pool, Mosconi Cup MVP
Dennis Orcullo
Winner of 10-ball event at Derby City, Winner at World Cup of Pool with partner Vann Corteza, Winner of US Open 1-pocket, 2nd at US Open 10-ball.
Lee Van Corteza
Won the China Open, Won theWorld Cup of Pool with partner Orcullo, Third at the US Open 10-ball, Second at the US Open 9-ball
My choice is Shane, but a strong case can be made for any of the five above. Most improved in 2013, and future candidate for player of the year is Carlo Biado.