D&D is always a safe bet because it's by far the most normie and famous. With newbies, it's tough to go wrong because they kind of "get" what's supposed to happen with it.
But if you do want to branch out, one system I like is Monster of the Week, which has a sort of base ruleset that have been then put into a variety of settings. The base Monster of the Week is modeled a bit after Buffy the Vampire and various urban fantasy works that have followed, you don't really have a class so much so as a character archetype. There's a Slayer, like Buffy, but there's also a Meddling Kid, like Scooby-Doo, and a bunch of other things like that. Part of character creation is to go around the table and decide how everyone knows each other and that's based on the character's archetype.
The actual mechanics are pretty straightforward. You basically have like half a dozen things you can do on your turn called "Basic Moves" and then some archetypes get a few more. So, your players can have a cheat sheet in front of them of what they can "do" and it helps keep things streamlined. The dice is just 2d6, so might be less intimidating than having to figure out the odds on a d20 versus a d4 kind of thing.
And the Monster of the Week setting specifically is pretty light hearted. So you don't have to worry about asking for some ultra-serious engagement from some people just getting their feet wet. One of the main actions is literally called "Kick Some Ass" and that's just how you say I'm going to do a combat action. Everyone can kind of treat it as extreme camp of a CW show or if they want to get a bit more serious, take it all the way to something like Supernatural or whatever.