I'd show them the original trilogy, and try to talk them out of watching the prequels.
I'll bash the prequels all I want. They stank. To be fair, ep 1 was "okay" if you judge it as a popcorn sci-fi adventure and not as a SW film. And there was probably nothing that could've been done to match the expectations of legions of SW fans anyway.
Having said that, they easily could've been much better than they were. All three films were poorly written. And ep 2 & 3 were very poorly acted, most likely due to using green-screens for practically all scenes. Not to mention that cgi typically looks like crap outside of cartoons and SW films have been no exception.
Prequels are usually garbage because you already know how they're going to end. If filmmakers make the mistake of doing a prequel, they at least need to put more effort into making it good than they did with the original film. But the SW prequels felt like less effort was put into them than the original trilogy. I dunno if they actually put more or less effort into the prequels, and I don't care. The results say "less," so thats how I judge them.
While we're talking SW anyway, I'll say this about the coming new trilogy: if they use practical effects and restrict cgi to when its absolutely necessary if ever, it'll look much better than the prequels. Plus the actors will have an easier time emoting correctly if they've got something tangible to act within. And if the writers have anyone but a brown-nose or a close friend to reign-in their worst ideas, they'll hopefully have something on par with ep 4 or 5. Lacking such a voice of reason to counter Lucas was why ep 6 was a disappointing goof and why the prequels felt aimless and dumb.