McLaren Park San Francisco in the day now called GlenEagles International. By far the most difficult 9 holes anyone could play IMO.

Gleneagles is as tough as they get. Another very, very hard one and absolutely gorgeous is Cabo del Sol, in Cabo, Mexico. Many drives over canyons and waste areas. The two finishing holes on the Gulf of California are incredible.

my vote is whitney oaks in rocklin. pretty tough for me anyway narrow and small greens.

Any Johnny Miller course!!!! The man is diabolical!