I think it depends on how much you have to lose? How much you want to (willpower)? And how much you can afford?
I started slim fast 10 days ago and I didn't think I had a lot of will power but I do seem to be losing weight and I still get to eat in the evening with my family. I'm not sure a total meal replacement would suit me but I may look into it after Christmas.
Apart from SW and WW what else have you tried before?