I don't usually get in photography type of debates because it's such a subjective field where beauty truly is in the eye of the beholder.
Nemesis is right though. If you are going to do some type of contest and maintain a level playing field, you can't give such a vague subject. As Nemesis pointed out, this really should be judged by multiple criteria. Is the picture clear? Is it composed nicely? Does it follow the assigned subject? Is it creative? etc, etc, etc. If you do a "car" theme, you will definetly throw out lots of the objectivity and merely get a bunch of people voting for the picture based on their own bias as to what their favorite car is (likely).
I've voted in all of the previous challenges and used some of the criteria I mentioned above. If they stuck to the subject and their picture looked appealing, they got my vote.
