I promised a Part 2, so here it is!!! The next great Sith Lord in the debate is...

Darth Vader~Though he was dismembered and marred during his first duel with Obi-Wan Kenobi, Vader clung to his life on the fiery banks of Mustafar. Though much of his potential for power as the Chosen One was lost with his injuries, Vader became a feared and powerful figurehead in the Galactic Empire. The Pre-Mustafar Vader was a Master in lightsaber combat, ruthlessly killing his way through the Jedi Temple on Coruscant, killing most of the Jedi present. Though his swordsmanship ability was limited after sustaining his many disfiguring injuries on Mustafar, he could still overpower an opponent with his overwhelming brute strength. He was a powerful Force practitioner, being highly proficient in the use of telekinesis to overpower his opponents, and force choke. A ruthless military commander, Vader would go to extreme measures to ensure the dominance of the Galactic Empire. I'd love to see how powerful Vader could become had he emerged victorious on Mustafar, but (unfortunately) that won't ever happen. Much like the Dark Lord Revan, he was a brilliant military commander, punishing incompetence very harshly to inspire fear of failure in the minds of his people.
If it weren't for Vader's power and leadership, the Empire (most likely) would not have existed.

Vader's Negatives...
The most obvious of Vader's negatives is that he lost a good deal of his swordsmanship and Force abilities when he was dismembered and scorched on Mustafar. He had a fierce loyalty to his master, which prevented him from ever attempting to overthrow Palpatine, although Palpatine himself remarked that Vader was indeed strong enough to defeat him. This likely prevented him from reaching his true potential because had he taken over the Empire by defeating Palpatine, his Force powers would surge with the victory (Through victory my chains are broken~the Sith Code). I believe that had Vader overthrown the Emperor, he would've become the most powerful Sith Lord in history.

Stay tuned for part 3!!! Thanks a lot for reading, I hope you enjoyed it!!!
Feel free to post comments!!!
(If there are any other Sith Lords that you feel should be in the running, just say so. I'll include them in the series if I agree.)

MTFBWY