I did weight watchers and lost nearly 50 lbs on it, I've kept the weight off for 7 months now. What I liked about it was that it delt with portion control and still allowed me to eat the foods that I normally like so I felt that it was realistic for me to stick with the plan for a long time.

The problem I don't like with most diets is that they are so restrictive that you really can't stay on them forever then you just gain the weight back when you go back to more realistic eating habbits.