A mixed bag. skewing toward the unusual or seldom-seen. I enjoy studying and learning about cars that are constructed with a strong mission or purpose in mind, such as:
1. Ease of manufacturing (usually coupled with low cost).
2. Ultimate speed or other performance measure(s).
3. Visual appeal (which is subjective, I know). Some cars meet two of those criteria, and very few, all three.
I have a strong dislike for cars that are vanilla, and am developing an aversion to kit cars that are clones of other kit cars (Kobra's, Flim-Flamborghini's, etc.), and, cars that are vanilla to the point of disappearing, and, the general rush toward bulking up vehicles with AWD and other "must have" features that 99% of car buyers were able to live without until relatively recent times.
My favorite puzzles to post, and to solve, are Hot Rods, Kustoms, coachbuilt specials, LSR cars, and home-built oddities that employ unique technology (real or imagined) or uncommonly pleasing aesthetic properties. I also enjoy the drawings and clay models of cars that were not yet finalized, or would never be finalized, by their creators.