RPGMemes

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.