In this battle, the answer should be obvious, but is in fact not.
Let us compare the two:
Personality
Darth Vader was once a Jedi, then he became the iconic figure he is today, then he sacrificed himself in the end. Orochimaru was a student to the Hokage, then he betrayed him, never again to look back.
I would call that a win for Orochimaru.
Weapons and Abilities
Vader may have the force and his trusty lightsaber, but Orochimaru, beyond a shadow of a doubt, has thousands of jutsu's at his disposal.
That makes two for Orochimaru.
Fan base
No question, Vader has this one.
Appearance
This one goes to Vader also, he is timeless.
Theme music
For Darth, it is easy, imperial march (not sure on title). Orochimaru's is more sinister (sorry i don't have a link), Orochimaru Fight Theme.
Sorry star wars fanboys, this one goes to Orochimaru.
Death (my choice)
Although Orochimaru's is cool, nothing can sway me from giving this one to Vader.
It appears to be a tie. Still, in a actual battle, Orochimaru would pawn Darth.