That's right, I'm calling upon all you Star Wars geeks and freaks. Who's the greatest Sith Lord in the Star Wars universe? Commonly titled "Darth," Sith Lords devote their new lives to supremacy, power, and the dark side. A quote taken from Wookiepedia sums it up perfectly:

"The Darth title was more than just a symbol of power; it was a claim of supremacy. It was used by those Dark Lords who have sought to enforce their will on the other Masters. It was a challenge—a warning to bow down or be destroyed."

―Kas'im^[src]

If you don't now about any other Sith Lords besides those mentioned in the films, or you just need to brush up on your Sith knowledge, check out this wonderful article on Wookiepedia.

My personal favorite is Darth Stryfe, who could quite possibly be known as the Arnold Schwarzenegger of the Sith. His power lay almost solely in his immense strength and brutality. But a picture could say it all:

-Holy shit!-

Your favorite Sith can be decided by their power, appearance, attitude towards the dark side and life, or something as awesome as their style of lightsaber combat (or any of them combined!).

Next time someone goes up to you and asks "What's your Sith, baby?," you can proudly proclaim your answer.

Darth Vader! Before those prequels where made... damn.. those were epic fail..

The answer you seek is Darth Revan.

What was fail about it? Before he put on the suit, or after he put on the suit and screamed, "NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!!!!!!!!!!!!!!"

It's a tough call. in terms of who was one of the most powerful Sith lords in history, Palpatine is somewhere in the top 10. But, if we're talking about our most fav sith lord.......it will definitely be Naga Sadov, the Dark Lord of the Sith that almost destroyed the Old Republic 5000 years before the I episode began.

Before the prequels he was this cool mysterious bad ass motherf*cker with the voice of james earl jones.. now he is a sissy girly boy who lookes like Hayden Christensen and cries "NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!!!!!!!!!!!!!!"

Man...  they even put him on the DVD of the Return of the Jedi at the end when Yoda Ben, and Anakin show up in Ghost form...

I agree NiKKoM. The prequels somewhat ruined his image as a powerful and wise Sith Lord. How is he supposed to become that from some emo kid that's powerful with the force?

Menago: I agree, that's a nice choice.

But i have to hand one thing to Luke Skywalker. Don't know how much you guys read about the fate of the New Republic, but about 20 something years after the Return of the Jedi, there was this Youhzann Vong (don't know if i got it right) invasion, them being basically a race from a whole different galaxy. They really kicked everyones ass, but was also the time when Luke reached his greatest force potential.

In what sense you ask? Well imagine Luke being able to create a black hole big enough to destroy an invincible alien fleet? Now THAT is mastery of the Force.

at least he was when i played as him

Both?

Since he was somewhat ruined.  I'll go Darth Bane.