Camaro, hands down! Not only does it have better times on the track and better lateral numbers, but it has a stronger heritage and following. There are many clubs, forums, and after markets products for camaros (not to say there are not any for challengers, just not as many). This makes owning a camaro as fun as owning a mustang (I have a mustang, and LOVE the forums available. I also own a 68 camaro, and love those forums just as much).
I guarantee resale will be much higher on the camaro in a few years.
My 2c