Well, I would not buy either car for itīs handling prowes to be honest. Mustangs, Camaros and Challengers are all about the engine. And which one will get you down the 1/4 mile faster then the other to be honest.
Even though the Camaro feels heavy, Iīve seen YouTube videos that show itīs the fastest 0-60 and down the 1/4 mile of the 3, execpt for the Shelby.
But the most important thing here is the fun to drive factor, if you like the Mustang better than the Camaro, then go fot it!! The Camaro might beat you on friday night drags, but if that is not paramount to you, who cares???
Get the car you like the most and enjoy