My answer would likely be different every day I was asked..
Right now, I'd go with a 1995 Lamborghini SE 30 Jota. It's my favorite exotic car, and I was able to see one in Miami Beach while vacationing there over Christmas break, with family.
There are so many exotic cars, it's really tough to pick just one. I've loved Lamborghinis since I was a child though, so I'd have to say they are my favorite exotic cars.