The Diablo, now with, what, I believe 600 hp from its 5.5 liter V12 and AWD?? Hard to compete with that. Although you have to be careful with it. In dropping the clutch from high rpms, in a Road and Track article they were able to fry its clutch in just two attempts!! Now that's impressive.
As for the Countach, I hate to say it, but even though it served as the be-all end-all of sports cars at some point in the early 1980's when I was growing up, today I look at them and find their appearance to be very.. dated, frankly. It is clearly a child of the 80's, and seems to have missed the "timeless classic" automotive design boat. And its performance is totally eclipsed by the sheer power of the Diablo.
In its own rite, the Countach is a classic. But there are cars that were made many years ago that still appear stylish and (dare I say) sexy today. For example the 1968 Camaro Z28. I honestly believe that this car looks (subjectively of course) every bit as good today as it did when it was first introduced 33 years ago. Much as I hate to rank on an exotic supercar while complimenting a relatively inexpensive domestic, I can't deny the fact that this is a prime comparison of two automobile designs, where one has withstood the test of time, and the other has not.
This picture of the Camaro does not do it justice. See the movie
Better Off Dead to see just how good this car is capable of looking.