My experience with diets is this: There is no magic diet or pill to lose weight. The healthy right way to lose weight is regular exercise, portion control, the right foods and dedication. You have to change your lifestyle.
I have been following this theory for 6 months now and went from 153 to 130 (I am 43, 5'4 1/2) I only have 5 pounds to go to reach my 125 pound goal.
I hit the gym regularly - 5 to 6 times a week, at least 30 minutes of cardio a day, three weight training classes and two pilates classes a week. I have gone from a size 10 to a size 4/6 and feel alot better. My muscle mass has increased and the shape of my body has actually changed and now has definition.
I eat 1,200 calories a day, that consist of fruit, veggies, lean chicken & turkey (I don't like fish, but if you like it that would be a good source of protein) I eat 5-6 small meals a day and stop eating when I first feel full. I drink almost a gallon of water a day and stay away from alcohol (except on the weekend!

) Losing 2-3 pounds a week is about right.
I tried the low carb thing once and it literally made me want to throw up. I just couldn't do it. I have heard that Nutri-system's food is expensive and tastes horrible, so I would stay away from that too. Weight Watchers I hear is great for some people that have a hard time maintaining their own diet, so you might want to try it.
I also stay away from all diet pills - All of them. There maybe some on the market that are fantastic, but I don't buy into any of the hype. Not only that, but when you stop taking them, does the weight come back? I am not going to take that chance. Besides, I personally don't think they are good for your body.
Just remember that dedication is 90%. It sometimes takes alot of self control to reach for the apple instead of the Snicker's Bar!