Cher has height on Madonna and I don't think she would be afraid to cheat, i.e. eye gouging, hair pulling, kicking in the groinal area. However, Madonna would have the obvious advantage in the hair pulling department because Cher's is so long and would be easy to grab. And, of course, Madonna is actually bald and wears wigs to hide it, so hair pulling would not affect her in a serious fight. Having said that, just watching both of them through the years makes me think Cher would pack a much harder punch. Yes, yes, I know Madonna is into fitness and has this image of being in shape, but I think Cher had a harder life growing up and would be a vicious fighter.
I say Cher beats the crap out her. However, I think it would be a hell of a fight and go on for quite a while.