Wow, that is a hard choice. I will have to go with 3 different ones I owned as each has very fond memories and each for different reasons.
First was a 1938 Ford Coupe that was chopped, channeled and had a 427 Cu. In with 2-4 Barrel carbs. The engine was balanced and blue-printed with pop-up pistons and 3/4 cam. Nice candy apple red paint job with pin striping. White rolled and pleated Naugahyde interior.
Second was a 1957 Studebaker Golden Hawk. Low to the ground and sleek, she ran good and fast, and wasn't too common so she stood out.
Third was 1964 Lincoln that I had converted into a pick-up along the lines of the Old El Caminos. It brought a lot of stares and comments, and I loved to go into an auto parts store and ask for a part for my 1964 Lincoln pick-up, then show them one when they said there was no such thing.