The problem with most diets is that they force you to eat in ways that you can't sustain long term. So when you go back to eating normally again, the weight comes right back. Your best bet is to make changes to your eating plan that you can live with forever. That's the best way to take weight off, but more importantly, keep it off for good.
Hope that helps,
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford