There is no real way to answer that, as the outcomes will mean different things to the victims. Scraping a knee might seem to be the worst to a child...
Usually, injuries that cause death would be considered the worst, but again, the severity of the actual manner of death could be seen in a number of ways. In some cultures, it is an honor to die in noble form - in battle, or a heroic deed. In others, death by your own hand or the giving up of life is a way to restore honor.