Why kill it fast as possible??? I mean this thing isn't a person and it's not your family dog.
Best and most practical method I've heard is to slice it behind the gills like your gonna chop off the head but don't go all the way through the spine. then throw the thing in a bucket of fresh water and let it kick and bleed out. Pretty much all fish taste better the more blood you get out of em.
Say a prayer to the good lord for it's suffering and harvest if that keeps ya from crying a river.
Other than that, I just bust em on the head like you stated in OP.