Mark Prior 
or
Wade Miller 
Well, let's think about it.
Prior: Prior has been with the Cubs for over five years, now, and has been hot or cold. He had his good years, especially 2003, and his bad, especially last year. But when he was good, he was really good.
Miller: Miller had many good years with the Astros. Again, last year was a down year for him, just like Prior.
Both of them were injured last year and not many people in Chicago have faith in either of him. They both have been good and bad, but Prior has been better.
Prior was surpreme in 2003. Great. Amazing. Fun to watch. Famous. He was unstoppable. People talked about him being in the hall of fame someday. He was loved in Chicago. Although people don't love him as much anymore, people know him better than Miller.
Overall, Prior has been a better pitcher throughout his career. My choice is Prior.
GO CUBBIES!!!