It's very difficult to pick a favourite corner because very few corners can be taken in isolation. To answer an earlier question, if PD took all of our favorite corners and bundled them together in one track they would probably lose their appeal. It's the speed and the line you're forced into them that make the difference.
I just did the Grand Valley 300km this weekend. The long right hander, the long left and the hairpin are the ultimate test of a car. Only the best cars can take the right and left at full throttle.
However, in 60 laps I do not think I took the two left handers after the hairpin correctly.
Nurburgring Nordshleife - I like the long clockwise corner between the start line and the finish line.
Tokyo - The right hand bend followed by the left under the subway bridge. That right hand bend has about 3 different, valid, racing lines, and if you and another driver take differing lines you'll actually overtake each other as you come out of it. The left is just a pure divebomb for all involved.
Le Mans - the section before Porsche which culimatines in the 90 degree, second gear right. Awesome!
London - The right, left, right at Haymarket. A very underrated course.