From similarity and differences of morphological, biochemical, cellular characteristics, biologist have constructed 'phylogenetic (evolutionary) trees' (who is most closely related to who, analogous to a family tree)
In the United States, lightning routinely kills more people each year than tornadoes or hurricanes. Tornadoes, hail, and wind gusts get the most attention, but only lightning can strike outside the storm itself. Lightning is the first thunderstorm hazard to arrive and the last to leave.
A hurricane is generally worse. Since they are much larger than tornadoes they can cause more damage and kill more people. e.g. A number of hurricanes have killed over 1,000 people, but only one known tornado has done the same. However, somewhat paradoxically, a tornado is more dangerous.