Hmmm, good question. I would say the most useable supercar has to be 997 911 Turbo but I do have a soft spot for the Gallardo Spyder- it's suprisingly practical with its 4WD system meaning that it's tractable in all weathers, you can lift the nose for speed humps at the press of a button and when the weather is a bit dismal you can drop the window behind the seats and still enjoy the active exhaust.
Although for thrills few things beat the current GT3. Except the GT3 I assume but I've not yet driven one of those.