Weight Loss Program- Which Program Is Really Worth It?

Many of my friends use a specific weight loss program to help keep them in shape. Each one of them uses a different program - trying techniques and foods that work for them specifically (after a long process of trying other weight loss programs that were simply scams or fads and did not achieve any long term weight loss for them.)

In this respect, how do you know that the weight loss program that YOU invest in will actually make a difference?