I have always said a 1970 1/2 Chevelle in Hugger Orange, with the dual white racing stripes down the middle. Gotta be a manual, and honestly the engine doesn't matter to me. Just give me one that has had a full restoration to brand new specs using the correct parts.
2nd place (if the lottery friend is feeling REALLY generous): same conditions above in terms of restoration, a 1963 split rear window Corvette.
A first gen RS/SS Camaro is something I have always loved.
I also have always liked the '67-68 Fastback Mustang, as well as a 2nd gen Trans-Am (loved Smokey and the Bandit as a kid).
I would have a hard choice though having to decide if I would want an "original", a modern update or a complete resto-mod.
If it was already a numbers matching vehicle, then I would keep it that way for sure.
If it had a replacement engine and such or was in bad shape already, sticking a built 427, better transmission, suspension and braking would be an option for sure.
But going full resto-mod with a modern V8 and other components would make a great daily driver with the looks of the early muscle cars.
But thinking about it, I thing as original as possible would probably be what I would want.