Luke Skywalker is in my humble opinion the best star wars character ever created because his pure heart and courage form the catalyst from which all other characters take their place. Just think what would have happened if Luke had never acted upon the desperate message of Leia's hologram. Exactly, nothing. Thanks to Luke, Han was allowed to become a hero, Obi Wan was allowed to finish out his mission, Leia was allowed to take her rightful place and Darth Vader was forced to pay for his myriad sins. Search your feelings, you know it to be true.
That's Darth Vader, without a doubt. Complex, misterious (well, he was untill someone decided to be clever and made three extra movies which I cannot stand), powerful, evil but turned out to be good after all. Plus the voice and all that leather... ;)
Jar Jar - no just kidding :P. I would pick Darth Vader because it was sad how he turned evil and he is really conflicted :(. He is a really good bad-guy character too and then whaen he dies it is really sad.
Oh there are so many to choose from. Especially choosing between Darth Vader a.k.a Anakin Skywalker or Obi-Wan Kenobi. But I'll have to say Obi-Wan Kenobi, it's not just because he is my favourite character, but because of what he went through. He had lost his Master at the hands of a Sith and then later on in life the boy he had trained became a Sith. I think that's all that I am going to say on that matter.