If you a fixated about gaining a six pack look to use a range of techniques. Just using spot training want gain you the results you are working for, in every exercise plan you need to use different muscles around the body.
The truth behind training is that if you want to get the best abs you have to lose weight and use an effective training method, same as if you want muscular gains you have to gain weight.
The best method for training is to recruit as many muscle fibers as possible using heavy loads, such as negative training, one rep max, squats, deadlifts, press ups and chin ups.
Increasing your hormone growth and testosterone levels by using different muscle systems, always include lower and upper body exercises during training.