Berserk summed up well.
BM is much harder to play well than a barb.
Hard to pick which is better for vs pking, if both player equal ability and eq I would say bm edges it as much more variety to their play and more ability to remove lots of the barbs bonus attributes.
In a straight up toe to toe fight barb will out damage a bm all day long, but if your dumb enough to let them then more fool you, if a tactical battle then bm should win.
Mass pk wise barbs are headless chickens, but bm need to be played strickly and is very much a team 1st player in mass pk.
So which is best in mass pk is determined by your playing style, loose cannon barb, team player bm.