Obviously a lot of people will choose Josh Hamilton (and rightfully so) but I'm going to go with Matt Belisle. Hamilton would be my choice for offensive player.
I have long been a fan of Matt Belisle. I loved the Mercker-for-Belisle trade the day it was made. I've always been a fan of his stuff. His velocity is starting to return to where it was before his back injury with the Braves, and his curveball has always been a solid pitch, but this year it looks sharper...you could really define it as a strikeout pitch now. With his size, I believe he has the durability to last over a full season. With his stuff and an extra year of experience under his belt, I am expecting a nice season from Belisle. 180 innings of 4.00 ERA ball and 140 strikeouts wouldn't surprise me at all.
Who is your breakout candidate?