I understand that Muzzin makes rookie mistakes, and that he has lots of potential, but those excuses don't give you top line time. I like Mitchell on the top d line; safe, sound, secure, primary goal is defense. But DS has said before that he can't keep WM on the top line because he is too old to handle those kind of minutes. So its a question of left handed youth, and between JM and AM, I choose Martinez. And more my point is that if we had to choose who to trade, Muzzin or Martinez, I'd choose Muzzin.
I also want to say that i don't think martinez has been given a fair shake had better minutes. In 2011-12, he was pushed down to third paring because of the left handed depth (scuderi, mitchell, and for a while JMFJ). last year he was pushed down because he was having a terrible season. but this year he is definitely more sound, but is is being marginalized because of conceptions from previous years.