NOTE: The Sith Triumvirate is not included. 1 Darth Sidious:
-Confirmed most powerful Sith Lord from various sources
-Defeated the second most powerful Jedi; easily defeated Darth Maul and Savage Opress
-Creating Force Storms capable of destroying fleets of ships and devastating the surfaces of planets
-Surviving as a spirit whenever his body is killed and traveling as a spirit across lightyears of space
-Making the planet Byss a dark side nexus
-Siphoning the life energies of the nearly 20 billion inhabitants on Byss
-Telepathically subjugating the wills of nearly 20 billion beings on Byss, erasing the memories of millions on Coruscant, and inducing fear into thousands of Jedi across the galaxy
-Projecting Force Lightning capable of scorching Sithspawn to ash, burning people to skeletons, and contorting lightsaber blades
-Causing the Force to become imbalanced to blind the Jedi's perceptions
-Hiding his Force sensitivity from the most powerful Jedi in the Order
-Perceiving events and eventualities throughout the galaxy
-Altering the tides of battles by influencing armies and fleets
-Controlling midi-chlorians to sustain life
-Moving his lightsaber too fast to be seen by Jedi who can react to lightning bolts and ships flying at sublight speeds 2. Darth Plagueis:
-Confirmed most powerful Sith Lord up to his time
-Complete mastermind of the Force and the Grand Plan
-Use of the force creates a "vortex of dark energy" unlike young Palpatine has ever seen
-His death created a monumental tremor in the Force
-His mere presence caused the coldest winter in Naboo
-Able to manipulate midiclorians to create and destroy life
-Capable of using Sith Lightning that burns people to ash and that spreads across an entire landscape
-His telekinesis can support and collapse caves, basically atomizes Maladian assassins, and even choke Darth Sidious
-Capable of summoning force illusions to even trick Darth Sidious
-Capable at moving at "lightning" speed and is considered a "master combatant" by Darth Tenebrous 3. The Sith Emperor:
-Most powerful force user up to his time (besides Mortis family)
-Beholds thousands of years of Sith knowledge and rituals, granting him nearly immortality
-Completed a Sith ritual that allowed him to harness the power of thousands of Sith Lords
-Capable of mind-dominating a strike team of powerful Jedi, and a young Darth Malak and Darth Revan
-Utterly destroyed the Dark Council in a "sudden flash"
-Possesses Sith lightning stated to be thousands of times the likes of buring ash, in which was capable of defeating Revan, an infamous user of Tutaminis 4. Darth Bane:
-The confirmed Sith'ari, who is said to have "perfect power"
-Complete mastermind and designer of the Grand Plan and the Rule of Two
-Perhaps has the greatest speed feat in the mythos, capable of dodging and blocking torrents of rain in a downpour
-Has extreme mental and physical pain tolerance
-Telekinesis can uproot a campsite, hurl a slab of rock that contained a Sith spell to keep it in place, and with amplified powers was able to collapse a huge power.
-Possesses lightning that can turn people and drexls to ash with a single burst
-Possesses the strength to rip open durasteel door's with his hands
-Capable of holding his own against Kas'im, and then later capable of defeating 5 Jedi, some of which were stated to be the best in the Order, while the Jedi were being amplified, with the aid of Darth Zaanah 5. Darth Caedus:
-Stated to being one of the most powerful Sith Lords in history and that he is superior to the likes of Darth Vader
-Achieved the most intense state of oneness in history, being described as being ""briefly transformed into the most powerful manifestation of the Force on record"
-Able to hold his own and severely injure Luke SKywalker, the most powerful Jedi in history, in a all out battle
-Possesses numerous unique powers such as mind-walking and force fold
-Possessed force lightning capable of turning people to ash on contact
-Has telekinetic abilities that can move 40 meter star ships
-Has defensive abilities that can tank ion canons and various other extreme blaster fire
-Possesses extreme pain tolerance to such a degree he continues to fight without an arm and a worthless leg
Darth Revan is stated in KOTOR loading screens to be Darth Malak's superior, however the player does not yet know of the Star Forge so they can't be taking that amp into account.
Jedi Revan by the end of KOTOR is stated by Darth Malak to be superior to Darth Revan, and Darth Malak implies with "I wanted to be Master of the Sith and ruler of the galaxy. But that destiny was not mine, Revan. [cough] It might have been yours, perhaps… but never mine." that even with his Star Forge amp, Darth Revan would be greater then him.
All in all, they are extremely close. Who is the superior? Don't really know.
He beat one of those Sith rancors with his bare hands.
"Left to guard the tomb serving as the resting place for its master, Marka Ragnos, the beast has dwelled in darkness for centuries. Legend tells that Ragnos beat his pet nightly, warping it with the Force until it was a creature of pure hate and anguish. Starved for unthinkable periods of time and then fed only blood, it is said to be filled with an unquenchable thirst for more.
Since the death of its master and its seclusion in the tomb, no one has seen the beast and lived to tell the tale. But the strongest Sith can feel its unnerving presence."
-SWTOR Codex Entry: The Beast of Marka Ragnos