1. The Sith Emperor/Lord vitiate
Why: He reconstructed the sith empire and ruled it for over 1000 years making him one if not the longest ruling sith of all time.The Emperor made Revan and malak obey to his commands later starting the jedi civl war and discovery of the star forge. He was eventualy defeated by the hero of tython.
Abilities: Even as a child the emperor was very powerful with the force he killed his father with just a thought.He used the force to drain the life and force from a plane to achieve immortatiltyt. The emperor could easily dominate the minds of others to obey him. He easily defeated revan with his mastery of telekinesis.
2. Darth Caedus
Why: There was hardly any match for caedus at his time he beat many jedi including master kyle katarn with ease. He discovered many force abilities that others had no knowledge of. The only one stronger than him was Luke skywalker.
Abilities: He was a master of using the force to control people to do his will at a young age he also learned to control animals and able to communicate to animals using the force. He achieved oneness with the force. He learned to shatterpoint he was able to see crucial weak spots in people and objects.He also learned battle meditation and was a skilled lightsaber fighter to be able to defeat jedi battlmaster kyle katarn.
Why:He Drained the life out of the massassi race and was able to matain his sprit in the temples of yavin for 1000s of years after he was dead.
Abilities:Kun was a master of the niman form and was skilled in jar kai. He was one of the best swordsman alive. He was able of emiting force blasts whcih could easly be used to defeat someone. He was able to attack other directly in his sprit form on yavin 4.He was also able to make students obey him in sprit form.
Why: Ragnos clamined the title dark lord of the sith and became the emperor he took vitiate as an apprentice and taught him further in the ways of the sith. Whule he was in power it was known as the golden age of the sith.
Abilities:Marka Ragnos was considered to be one of the most powerful sith of all time even after death he managed to keep his sprit alive and kept growing power he was nearly risen again on korriban but the jedi jaden korr defeated him.
Why: Known as the lord of hungar. He fed on force energy Devouring people and planets he had the ability to destroy the galaxy if he became strong enough.
Abilities: He was able to consume force he used and aggresive one handed lightsaber style to defeat enemys. He was skilled in many dark side force powers and could drain the force of people around him. He was defeated by the exile aboard the ravager.
6. Darth Revan
Why: Revan was the most powerful jedi of his time it was his leadership that allowed the republic to defeat the mandalorians in battle. He later became a sith sparking the jedi civil war on the galaxy he went to the star forge single handly and defeated his old apprentice darth malak and saving bastila shan. After the star forge he went into the unkowen regions back to defeat the true sith threat that only he knew about .
Abilities: Revan was both strong with the froce and a lightsaber. He was one of the best tactians in all of the jedi. In revans time there was hardly any match for him besides the sith emperor himself who traped him in statis at the foundry.
Why: He had the potiential to become the most powerful force user ever. He defeated both Darth vader and darth sidious by himself not even luke did that luke needed vader to help him. His true self died sacerficing himslef for the rebels later he came back as a clone beating vader again.
Abilities: His power was endless useing lighting and throwing AT-STs around he brought down a star destroyer with the force . He was able to disenigrate stormtroopers with a wave of force known as repulse.
8. Darth Sion
arth sion or lord of pain was unstopable the only thing that could kill him was himself he was able to use his damaged body to keep regenerating himself through the force he died cause of his feeling for the exile.
Abilities: He always needed hatred to keep his body together as long as he hated he could keep rehealing his body making him invincible. He used an agreesive lightsaber style to beat his enemys.
9. Darth Plageuis
Why: He had the ability to create life he used this ability to create anakin skywalker inside of shimi. He taught darth sidious the ways of the force and the dark side.
Abilities:He was the master of the unnatrual aspects of the force He is best known for the ability to create life. Plagueis used 2 lightsabers in combat. He was able to asorb blaster bolts than channeling them into force lighting. He could save other from death but not himself.
10. Darth Malgus
Why: He was the leader of the force that sacked coruscant . He later made his own empire which could have worked out rather good It took 4 of the republics top heroes to kill him and even then he still never died he was only defeated. You could probably say he was the republics most wanted.
Abilities: he was a sith warrior. He used an aggresive 1 lightsaber form but on certain occasions he used 2. He had the ability to become invincible for short periods of time ( as seen at end of false emperor)
People that cam close but didnt make my list
Well this is my list it took me a great amount of time to make after an hour i got sloppy with spelling/ No hating these were my opnions of who to put where if you disagree so much make your own list. Also i hasnt played inquistor so i really dont know much about darth nox. Also i might make a jedi one sometime but this is my sith list enjoy.