Either 3d6 straight
Or 2d6+6 straight
The Rules Cyclopedia had some interesting methods for generating “higher level characters”: roll 5d6 and add 60, then distribute the total among the six attributes as desired. Or, just give the players a certain number of points between 60 and 90 to distribute. This would be very similar to how character stats are allocated in the infinity engine games—Baldur’s Gate and Icewind Dale.
The Mentzer Basic Set (Red Box) used an array for the sample characters (including the “poor but famous fighter” in the intro adventure): 17, 16, 14, 11, 9, 8
For Demihumans, it was 16, 14, 11, 9, 9, 7