The question posed got me thinking: Since there are quite a number of people falling for traps, it could be an indication that the face is what people go for at first sight. Of course, that is assuming the trap does not have attention catching tits or ass. :D
In reality, the angle in which one looks at a female plays a part too. There have been many instances in which I only caught the back view (including ass) of a female, especially in crowded areas.
That is true because the face is what I notice first, but when it comes to my preference I'd have to go with the breasts, the size doesn't matter as long as they're perfect. ^_^