RPGMemes

Honestly, the system you run for new players should depend on who those players are, their preferences, and comfort levels with related things you can use to judge their preferences. A group of hardcore eurogame boardgamers are going to be a lot more comfortable learning a complex rule system than my in-laws.

I don't think DND or close relatives is as good a first system as people think it is. It's very idiosyncratic. It wastes a lot of time with stuff like "8 is -1 and 14 is +2". But mostly I don't recommend it because at its core it is a resource management game, and that's not what most people imagine roleplaying is about. It will teach people bad habits, or at least habits that don't translate outside of DND + their group very well.

I like Fate. I think Fate is more intuitive and rewards creativity more consistently. You don't need to read long lists of classes and spells. It does, however, ask for a lot more creative input than DND does. You can't just be "Bob the fighter" and go. But it's a lot more rewarding when it does sing, IMO.

Whatever you and your group are interested in or whatever the GM has most experience with.

Personally I'd go with Blades in the Dark. It's great for teaching people good roleplaying habits and has advice like: drive your PC like a stolen car. The system is built to run on minimal prep with every pc action pleasing or upsetting another faction in the city everyone is locked in so you just need a few minutes to think before each session to work out what's happening next. It's very player driven and good for practicing improvisation. Plus the setting is instantly interesting (haunted Victorian London meets Venice) and I love flashbacks and clocks.

Other than that I'd recommend running a pre written module or two rather than making your own setting as it's too easy to fall into railroading players to tell your story.