I'm a bit surprised that Empire was so quickly pushed aside on the podcast and hasn't been discussed here. Particularly since the argument seemed much more based on influence and impact than quality, I think it's important to point out that The Empire Strikes Back contains perhaps as many things that live on in public consciousness as Star Wars does. (When people think of iconic Star Wars moments or information, my guess is what they think of is 40% from Episode IV, 40% from Episode V, 10% from Episode VI, and 10% from all other movies together.) Paul mentioned that Star Wars information is so ubiquitous that most people know that Darth Vader is Luke's father without seeing any of the movies. But again, that information isn't presented in Star Wars, but rather it's given in The Empire Strikes Back. And while Star Wars had John Williams give us the main title theme, the force theme, and Leia's theme, it wasn't until Empire that we got the Imperial Death March, which may actually be more well-known than the others. Episode IV lacks Yoda and Lando, and the only lightsaber battle in Episode IV kind of blows compared to what the series would later give us.
And to be honest, the principle of this original vs sequel argument isn't one I've been very consistent on, as I lobbied hard for Toy Story despite accepting that Toy Story 3 is a better film and I decry The Godfather Part II for retreading over much of the same territory as The Godfather, yet I also voted against The Lord of the Rings: The Fellowship of the Ring because I think it's the weakest of the three films. So if this were asking whether I'd pick Episode IV or Episode V for inclusion (as Amy once did on an early episode of The Canon), I'd be more torn. But if we're using Star Wars as a stand-in for the whole series, then clearly it belongs on the list. However, I'm just judging it on its merits as a film, so though it still makes my list, it won't be as high as The Empire Strikes Back would be. (I'll probably have Star Wars in the 50-60 range when it's all said and done.)