I'm a mustang guy. They don't start as much from the showroom, but they have so much aftermarket potential with every model since 1979.
My '86 5.0 GT had 225 HP from the factory, and with with my 331 stroker it was easily 450hp. It's surely not the prettiest, nor the highest potential if you had unlimited $$$, but for the average Joe with some greenbacks to burn on their car, it's a great option.
IMO, muscle cars started from guys tinkering with mid-level cars and making them quick, the factories paid attention and started outputting greater potential cars. The Mustang (even though technically not a muscle car) carries on that tradition well.
Aaron