Hanson easily. He may not be in the bigs now, but there's a strong chance he may be there by mid-season. And when he gets there, he get wins, unlike Zimmerman who with struggle with an uneven offense.
Here's what a friend of mine thinks of him. http://baseballinstinct.com/2009/02/17/
When you want a top arm, Hanson is a surer bet than most.