Derozan. It is comparing apples to oranges. Butler gets the benefit of the doubt for playing a role, any role in a playoff series.
If Derozan stays at the level he's at now, and Butler doesn't improve, Derozan is the better player. Derozan staying as a top 15 scorer in the league is better than being a tier 2 defensive stopper. The opportunity for Butler to show his offensive arsenal is right there waiting for him, Chicago is desperate for someone to step up.