Gotta go with the original. As great as Empire was, it didn't have the impact of the original, which totally remade the "look" of visual science fiction. Consider the smooth curves and stilted presentation of spaceships and other gagetry in films just a few years older with the "hardware look" immortalized in the Millineum Falcon and the "realistic" movements of the TIE fighters, and you see the sea change. (OK, I know that's not the way TIE fighters or anything else would really move in a vacuum, but to our earthbound, atmosphere-soaked perspective, if was far more viscerally "real" than the "spaceship on a string" stuff that preceded it.)