I purchased my 2011 V6 Mustang brand new (ordered it from the factory). I cross shopped with the Camaro but I felt the Mustang was just a better bargain, I liked the interior / electronics more and the visibility was much better than the Camaro. I've had it over two years now and haven't had any problems.
If you are going to go the V6 route, I'd suggest getting the manual so you can really get the most out of the engine.
I have been a little disappointed with the in-city fuel economy. I do mostly city driving and I'm averaging about 20 MPG, which is pretty close to what the V8 guys get, I hear. On the highway, it gets very good mileage (around 30 MPG, depending on your speed).
The Mustang offered everything I was looking for (300+ hp, beautiful looks, lots of features (HID headlights, voice commands, leather interior, etc) for the best price in the category. The only thing I wish it had was that V8 rumble.