The Boss is a better track car, the GT500 a better cruiser. Though I would choose the GT350 over them. My favorite of the current Mustangs is the 07-08 Shelby GT/SC. Classic lines and tons of horsepower, very few around.
550 HP in a car capable of 1G lateral that's cheap to maintain.
The independent rear suspension would be nice, but was determined to be not worth the cost.