Wolverine vs. Superman?

A buddy of mine contacted me in this week & asked me a question. If Wolverine & Superman ever got in a duel, who will win. Answering his question is not easy for me being a Wolverine freak. So I told him that I will hear from you guys & ladies on what you think. I know in the comic universe it will not happen due to DC & Marvel not mixing but I believe it will be an interesting fight. Please help us out here. Thanx