I have several Sigs, including the P220, and also have several M&Ps, including the 45 ACP. Accuracy and shootability are non-issues. The main difference in operation is the trigger pull on the first round. The striker fired M&P has the same pull for each round fired, while the Sig has a heavy first round pull. When ATV riding, the guns rest equally well on the hip. The big difference is after getting off the quad, my pants fall to my ankles with the Sig, while the M&P allows the pants to remain around the waist. Suspenders are worn with both pants these days.
My point is, is that sometimes body styles of a person have as much to do with the gun you carry as much as anything else. For me, the lighter polymer guns make a difference when actually standing or walking.