Favourite Dark Lord?
Hands down Darth Nihilus. Honestly, he could consume the entire life-force of a planet just by using his own power (unlike Vitiate who used rituals and sorcery). Nihilus' power I found was so great that he practically became the Darkside + his mask (which became an artifact) was able to grant a non-force user, the powers of an apprentice level Sith (or Jedi). Hard to beat!