Camaro. Now, I'm a little bit biased since I work for a GM dealership, but I'd have to say the new Camaro looks better than the Challenger IMO. The Challenger is a better example of retro styling as it retains the original lines while still looking modern, whereas the Camaro is a new look with a few retro styling cues tossed in for product familiarity.
What I really like about the Camaro is what I see in it's performance potential. It's built on the same platform as the Pontiac G8. I've driven the G8 GT and it really moves and handles well. I would not be surprised if the Camaro's handling is better, if not similar, and if GM eventually offers it with either A) the same 556hp LSA engine as the new CTS-V or B) the LS9 for the Corvette ZR-1.
If it were between those 2 id have to go camaro. the challengers heavy, not that the camaro isnt, but I also love the way the camaro looks and it will be faster, like I said id go camaro if those were the only 2 choices. my real choice would be and is to save about 10-15k and get a used 01-04 z06. lighter, faster and better handling that either of those cars. I dont have a use for and dont forsee a use for more than 2 seats, its just me and the GF if we have visitors we use her car. I will have a z06 in probably a year of so.