Orcs, definitely. Trolls are solitary creatures who can only be harmed by acid or fire (otherwise, they simply regenerate). Everyone knows the a true "metalhead" cannot be harmed by acid, but they can taste colors. Goblins are too small and easily destroyed by a punch to the face to be a true "metalhead". Orcs- now there's a group who, by nature, roam in makeshift mosh pits. You don't ever fuck with a group of orcs (unless your character has some pretty sweet magic items and/or spells).