Who is more famous Darth Vader or Captain America?

Answer 1

Prior to 1977 and the release of Star Wars the answer would have been Captain America (the comic book was created in 1941).

However, even though awareness of Captain America has increased again since the release of both Captain America and The Avengers movies; Star Wars and Darth Vader merchandise continues to out sell Avengers and Captain America.

Also, Darth Vader shows up in far more pop culture cross over references, jokes and cultural notations outside of his genre of origin.

So, I would have to say Darth Vader, though it's still a subjective opinion.