Offensively, I would be open to bringing in Martin. He would take some heat off of Dirk. I remember Dirk complained a while ago how he's tired of having to do all the scoring. That would also make Dirk a little more fresh for the Playoffs, which counts. Defensively, idk about Martin.
If Martin is unattainable and it had to come between Iggy and Butler, it's tough, but I would go with Iggy.
http://www.basketball-reference.com/...iguodan01.html
http://www.basketball-reference.com/...butleca01.html