Fighting Fantasy - The Introductory Role-playing Game
Might I suggest: Fighting Fantasy - The Introductory Role-playing Game
A group of friends and I used to play this in the school playground around 1984-1986. It was simple, fast and had the great back-story of the Fighting Fantasy game books to base adventures in.
I played Basic D&D, AD&D 2nd Ed, Traveller, Runequest, Tunnels and Trolls, MERP and Call of Cthulhu. Of them all, I always went back to the FF book mentioned simply because I inevitably got bored with the other systems' desires for complexity over efficiency. The only other one that came close for speed of play was Tunnels and Trolls - which, incidentally, had some great humour in it too.