Raiders... is the better movie. Star Wars has had a huge impact on the way many people see science fiction, but as a film, as a story, Raiders... is superior.
Part of my opinion is based on the fact that Raiders... did not need sequels (although I am glad that they did a good job with Last Crusade, though Temple... and Kingdom... should never have been made). Certainly, the Star Wars trilogy can be viewed as one large 3 act play (composed of 3, 3 act plays which appeals to symmetry), however, even when viewed as such, they are a mish-mash of conflicting sub-plots, story inconsistancies, overly complex character interaction, uneven direction and acting and rests on a backstory not clearly thought out.
Raiders... on the other hand (despite some rather obvious flaws) is nicely self contained. The backstory is nicely summed up in the first 20 minutes; we learn all we need about Jones and his world quickly without resorting to long and tedious exposition (unlike Star Wars) in a wonderfully concieved and directed action sequence. The story hangs together much better and makes wonderful and appropriate use of pulp and adventure genre cliche. You know there is going to be a jilted woman, because there is always a jilted woman in this sort of story. The story and the film play to the audience's expectations while remaining fresh and interesting. The direction is great. There is inspired use of static shots and close-ups to imply movement, emotion and detail reminescent of pulp comics and old film serials. All around, Raiders of the Lost Ark is a great film that has not only aged well, but continues to impress on every viewing.
That said, Star Wars will probably win.