I used to use GURPS. What I liked about it was that it was super easy to introduce someone to the base rules. You have your stats, and when you try to do things, you have to roll a check against those stats, and the 3-18 bell curve makes it straightforward to identify "is this a good idea, can I pull this off, is it worth the risk?" Meanwhile, there's also a rule for everything. You can play it by ear a little bit early on, but if you have a long-running campaign, and you realize that something is a consistent concept in your campaign, you can pull some rules into your campaign that can actually make that part of your world seem more unique and interesting. The pitfall is that there is a rule for everything and the game itself doesn't actually do that much to guide improv, and is mostly focused on conflict resolution (the same criticism I have with Dungeons and Dragons). These days, for the things I'd use GURPS for in the past, I use FATE, and for anything else I look for interesting systems, or a PbtA game with the theme I want
But I still love that 3-18 resolution dice bell curve. I even know a Dungeons and Dragons DM who straight up replaced D20s with 3d6. I don't know that I agree since Dungeons and Dragons is much more "chaos simulation" but he truly appreciated that critical rolls were less frequent and felt more exciting with the 3d6