I'm actually split between the two but I like Chevy a little more than Ford so I'd take the Camaro. Watch the rear visibility in the Camaro while test driving. The 2018 Mustang looks sweet though with a 0-60 under 4 seconds and that cool gauge cluster screen. I think it comes down to your taste with sports and muscle cars. You can't go too wrong unless you get an automatic. Take an extended test drive of both cars.
I think the Mustang is more like a muscle car and the Camaro is more tossable.