Tri-Disaster is going to be more of a PVP action if you compare it to Blizzard II. Tri-Disaster can be used with Swiftcast to bind mobs or players to run away, so can Blizzard II (and won't require a target to do so but will only work in melee range). Basically Blizzard II > Tri-Disaster but Tri-Disaster is more safe to use and depending on the situation has potential to land on more targets as you generally wouldn't run into the epicenter of danger in order to thwart it.