There are few cars built in this century and even fewer muscle cars that I would like to own, so even if I could afford one, I would not want a muscle car built in this century.
I can understand the appeal of the Challenger as the older models are one of the few muscle cars that don’t make me wrinkle my nose, but I don’t like the updated look; the Camaro and Mustang have better execution of the retro look. In fact, I think the new Camaros look the best of any year for that model.
As for Mustang, the absolute only way I would ever consider a Mustang is if it were a Roush or Saleen. Regardless of year/generation, the Mustangs are nothing but looks and tire smoke unless you replace a fair portion of the car (the suspension, half of the engine, a few things in between…) with aftermarket stuff.
If I wanted American V-8 power, I would go with a Corvette.
If I wanted a 2011 performance car, I would go for a Nissan GT-R; 530HP and handling!
However, that is my opinion based on my tastes. If you like the new breed of muscle cars, more power to you.