Different plans address different problems.  If you’re a junk food junkie, South Beach might be great, because it forces you to cook a bunch of fresh foods.  If you’re a carb addict, Atkins would force you to let that go for a while.  If you’re too busy to prepare food, a meal replacement plan could be your friend.  If you’re any sort of an emotional/stress/compulsive/bored eater, Medifast is great because everything is limited, even celery—there is nothing whatsoever that you’re allowed to binge on.
There are countless diets available.  I got lucky when I chose Medifast.  My selection process went like this:  I’ve done South Beach and loved it, but I’m too busy to cook that much. What else is out there?  Oh, I have a friend who’s lost about a hundred pounds, ask her what she did.  Medifast?  Oh look, packets!  Neat.  Sign me up.