The leadership thing is interesting... Moe brings energy, but it isn't always positive or level-headed.
Duncan is going to be 23 years old, mature, knows what is going on. Could provide some of that steadiness in terms of leadership. For example, Duncan was the guy who stood up and convinced everyone to get on the plane and fly to D.C. the next day.
I don't really see any way that Duncan doesn't play major minutes, especially because of how much three-point shooting Michigan lost last year.
Simmons definitely will bring some experience and leadership at a position where you need it, but still have to see him in a U-M uni.