Diablo hands down. The Diablo is a true driver's car. No traction control. No ABS. No power steering. The Porsche is a well balanced, well manered sports enthusiest's car that is so driveable, the driver becomes disconnected. You dont have to think using a Porsche, the car can pretty much drive itself.

Have you been inside a new Porsche? Whatever they use for leather smells like plastic. The Leather in the Diablo smells like real, leather.
Yes, the Diablo has all its own idiosyncracies, but that is why I love it. When I step on the gas, I hear all the passion that went into building my car, by hand, one at a time.

The Porsche is a good daily driver, but for that, there are a lot of choices. You could buy a mini at a quarter of the price and have just as much fun.