I've gotten the best results by using the T-Core. As with anything, of course, it only works well with consistency and not an "on - off" workout mentality. Give it a try, but be sure to refrain from eating foods high in carbohydrates after 7 pm.
While I don't have a six pack, right now it's only about 2 and a half. The one thing I've learned is to not underestimate the role that nutrition plays in fitness. It's critical to eat all the right foods at the right times. Other than that, lots of exercise will probably get you there.
I'd agree that it is a combination of cardio (to lose fat covering the abs), ab resistance training (to strengthen the ab muscle and make it more prominent), and diet (to reduce fat and help build the ab muscle). Other factors would be important, but these three carry the most weight.