Having used all 3 methods
Wiimote = 9 (point and shoot - fast, natural, and very accurate)
Mouse = 8 (moving hand and shooting - fast, not quite as natural, but mostly accurate)
Pad = 5 (moving thumbs and shooting - can be quick, but clumsy, and less accurate)
Saying this though if someone spends a lot of time on anyone of those controls they will get quite good. But most people are so used to a mouse that at some level it will be better than anything else a person uses