Exar Kun had no foe strong enough to defeat him and easily took out the Jedi Grandmaster. He was capable of removing people's shoulda from their bodies. Darth Sidious could pass his soul onto others and created wormholes and force storms. Darth Nihilus was a walking black hole. He killed Sith and Jedi alike. Nuf said. Darth Revan was a badass who turned Jedi at will.