I want to drive the new Camaro SS and Challenger R/T. A friend has a '11 Mustang GT and it is an absolute missile. It's on the big side too if you are comparing it to the older models, but it handles really well for a car of that size (and for any size, actually) and is very comfortable and easy to drive. I found it to be more comfortable inside and easier to control, both in a straight line AND around corners, than my old 2009 WRX. So what if it's big? The car performs. Did I mention that it is FAST?
The only "seat time" I've had with the Camaro and Challenger occur on Forza 4.
Looks-wise, my hands-down favorite is the Challenger. I'm not sure what it is, but it evokes all the awesomeness and insanity of those old Mopar musclecars of the late 60's-early 70's better than the other two pony cars. The wife even likes them and said we can get one in a few years when we have a bit more money.
And remember kids... there is an aftermarket for a reason. You can go in any route with any of these three cars as far as performance goals go.

