If I had to give a game to someone who was not familiar with rpgs I would give them a copy of Basic Fantasy. There are a few reasons for this.
1. Basic Fantasy is an easy system. It mimics the Basic D&D rules while adding ascending armor class, The rules are a quick read and concepts are explained well.
2. Since Basic Fantasy is from the D&D family, it will give the new player exposure to the common tropes and rules of role-playing. They will learn about classes, levels, orcs, saving throws, xp, etc. They will understand what old-school grognards as well as 3.X players are talking about.
3. The books are inexpensive and pdfs are available for free. The rulebook can be purchased for $5. For less than $10 I could give them the rules and an adventure.
If you haven't checked this system out, here is the link to their website: