It depends on how much you need to lose. If you need to lose a lot, then probably weight watchers. I was on weight watchers for a couple of months and only lost 5-6 lbs., but I only had about 20 to lose. So it didn't work that great for me, but it def worked well for the people who had more to lose. Also, the weekly meetings are good for support and motivation.
The South Beach Diet is good for losing a few pounds, but I found I needed my carbs, so I didn't stay on it for very long. I'm very active though and need carbs for energy, so if you're not very active you may be able to handle giving up carbs??
All in all, weight watchers is prob a more balanced and healthier diet in the long run. I think it teaches you how to make better food choices.
Good luck!
Oops, just noticed the name of your post! Duh!

Oh well. I still agree with the others - weight watchers is the way to go.