I don't have a single answer to this.
The thing is, games are subjective. The reason Husbit didn't join our Aberrant game is that he doesn't enjoy superhero-type games - but he does love horror, particularly gothic horror - particularly Ravenloft. He also doesn't love the mix of high fantasy and dirty sci fi that makes up ShadowRun, would rather play either separately; I know a lot of people who feel they shouldn't mix. But I love the game so would want to share it.
I think it makes sense to pick a game that's easy, because if I'm giving someone a generic game rather than something handpicked for that individual it's because they're new to gaming and I want to ease them into it. So what to pick?
I started on Buffy and it's pretty straightforward, so for anyone who loves the show - or at least likes the idea of it but maybe is too young to know it - I might give them that.
I nearly started on WFRP: friends of mine wanted to play but no one wanted to GM so they gave me a copy and asked me to, and I wrote a little scenario involving a goblin attack in a cave (which is probably actually in the book...), but they never got around to organising the game (and never asked for the book back, which is the story of how I earned my first roleplay book). It is simple enough, and if you've played Fantasy you'll be familiar with the world - only now they've trashed that and rebuilt some Age of Sigmar thing I don't know about. So maybe I wouldn't give that one to a beginner any more.
Oh, I don't know. I'm not very good at this. I'm a player, not a GM, and this sounds like a question for a GM :-/