TVR King
Sorry, I've got no good news for you. Although some people swear that you can pick your prize car, I have yet to see that method actually work. Basically, the theory is, if you hit X right when the shadow first touches the car you want, you will get it. Now, the response by people, when this doesn't give you the car you want is "you must have done it wrong". <shrug> My guess is, it is random. All things being equal, I'd guess your odds are 'bout 1 in 4, but that doesn't guarantee you a win.
I myself have gotten lucky at time and gotten the car that I wanted right away, but more often than not, I end up with something else.
So, the long and the short of it is, it's random, so best of luck to you.