Mechanical broadheads especially Rocket Hammerheads are better in my experiences than fixed blade broadheads.  I have never lost a Pope&Young or Boone&Crocket deer while using a mechanical broadhead.  Its about shot placement and the Rocket Hammerhead 2 inch cut causes more hemmoraging than the inch or so fixed blade.  If you hit a big 300lbs deer in the shoulder, I don't care what you use you will get the same result.....nothing.  I get the same penitration using mechanical's as I do fixed bladed heads.