2012 Camaro SS, 2012 Mustang Boss 302, or 2012 Mustang Gt Premium?
Performance wise, the Boss.
However, there are not very many drivers who can extract all the performance out of a GT that it offers. So from the practical point of view the GT is the best choice.
But most of that is because around here, there just is not enough of a straight away for the Boss to do what it does best.
My choice in fact is not on your list, and that is the new SHO. If you want luxury, performance, speed and handling - give it a look see.