In the vast majority of cases yes a cut on contact head will give you the best penetration. However, penetration is only one factor in killing an animal. You want good penetration coupled with maximum tissue damage. Good penetration cutting less tissue doesn't do much good.

With the speed and efficiency of today's bows it is hard to argue that you can't get good penetration with most of the modern broadheads out of a well tuned bow. So, you want to make sure you get maximum tissue damage with that penetration which usually means a wider cut and/or more blades. Since most COC heads are longer in the ferrule that means more to steer the arrow off course. This is why I don't shoot them. I like as big of a cut as I can get out of my set up.