I haven't done SW, but I have done WW, Dukan, and I'm now doing boot camp on here. These are my thoughts:
WW was great for that ability to eat whatever in moderation, but it didn't always lead to the best choices. I still ate lots of refined sugar and processed and artificial foods. It was the first proper diet I ever did and I was only interested in losing weight, and I was very successful. I found the weekly weigh-ins gave me a buzz.
Dukan was bloody miserable. It was in preparation for my wedding, I took it a bit too far, and I don't think it's sustainable.
Low carb is my favourite. I truly believe in the science behind a low carb high fat diet. I don't get hungry because the fat keeps me full, my food is delicious and healthy and varied, and I feel really good. I was drinking three or four Diet Cokes in a day and eating chocolate, cake or biscuits after every meal. I stopped all that on the fifth of January and I haven't slipped once. I feel amazing. I have more energy, I don't get bloated or uncomfortable, and I have lost at least a stone. It has been liberating to sit down in the evening pleasantly satisfied from my dinner, enjoying a cup of green tea, without wondering what I could eat next. I simply don't think about it anymore.
I think that, at some point in the next few years, SW and WW will have to change. There is too much evidence now that fat is healthy and an important part of our diet, and that sugar is the real enemy.
Obviously, you have to decide what is sustainable for you, and I totally understand why people with families find SW to be an appealing option. Saying that, I hate the culture of 'syns' and 'naughty' foods. If you're really thinking about low carb, I would read Escape the Diet Trap and look at some paleo resources as well, like Mark's Daily Apple. Once you know the truth about fat, it makes SW and similar look pretty behind the times.