If I had to choose one, and I couldn't sell it to buy others, and I had to live with it...
http://www.diseno-art.com/news_content/wp-content/uploads/2012/06/2012-Aston-Martin-Vanquish-8.jpg
Aston Martin Vanquish. Best all-arounder exotic, IMO. And drop-dead gorgeous.
If I could have cars for toys, or multiples, then a Caterham 500R, Ferrari 45 Speciale, Lamborghini Sesto Elemento, Pagani Zonda Cinque, etc. But of them all I think Aston delivers the most complete package in what I want from a single car.