Vader, for all his power, is still human and still has compassion (much as he tries to deny it). Sauron is a borderline satanic entity with no scruples or humanity. There's no way Vader could take him.
That being said, it would be a tremendous fight to watch. Vader would go down, but he'd make it as painful and difficult for Sauron as possible.
Wasn't it a human who defeated Sauron in the first place? It was only after Sauron cut through about a hundred men, but a human still defeated him. You have to keep in mind Vader is technologically superior, what with his lightsabre. I'm not saying Vader would win indefinitely, but one wrong move from either of them, and the other could end it.
Me and my sister actually had a really interesting discussion about this once, or it was more like Which of the most know dark lords is the greatest? Our conclution was Sauron (or more like the Ring), cuz let's face it, no dark lord could beat him in the long run. Neither of the dark lords could ever bring themselves to destroy the ring and thus Sauron ( or the Ring) sooner or later would stand as winner. But i really like the idea, you could really go back and forth here!
Holy, amazingly incredible! Sauron and Darth Vader look stunning and The Landscape is incredible. The poses, action, armor, light saber, ledge, atmosphere, snow, effects, sky, clouds, textures, concept, composition, uniqueness, style, lighting, colors, and other details are also spectacular! Excellent work!
Oh come, Sauran is pure evil, he becomes disembodied even after being killed. His power derives from his very nature as a "fallen angel" or Maiar in the Tolkien verse. I don't think a Jedi/Sith would stand a chance against him.
Maybe, but knowing both of them got beaten by their own enemies and the fact that their enemies now control every thing they pursued. Allied now and they may have the strengthen for vengeance. A rod alone is weak, but tied together with others, they are strong as one.