What is the worst kind of damage that a tornado can cause?

The worst type of damage a tornado can cause is EF5 damage.

An EF5 tornado completely annihilates even the strongest homes, wiping them clean off their foundations. The few trees that remain standing are stripped of their bark with only stubs of the largest branches remaining. Asphalt is torn from roads. Reinforced concrete structures are heavily damaged. Cars are thrown great distances and left as pieces of twisted metal.