If you had never heard of Star Wars and just watched all six films for the first time, which one do you think you would vote the best.
You have to take away any preconceptions of having 3 original films, and 3 new films, and just look at each film on its own merit. You can assume you will watch the re-mastered versions of the 3 original films.
I haven't counted The Clone Wars animation, as its not as mainstream.