This is a tough one for me, you either go for a guy whose exceeded expectations or a guy with consistent track record. Im going with Lester, one of the best playoff pitchers having a great year on a very good team. Tanaka was a close 2nd though.
I think Darvish is the most talented guy left here, but he needs to regain his 2014 form after the missing all of last year, and I think that'll come next year, but I need to see it. Lester has been the most consistent the last few years out of everyone left.