Any diet will work provided you keep at it. The trick is to understand what your personal issues, fears and weaknesses are, and also what you are likely to be able to sustain over the longer term.
For example, I am addicted to chocolate. Seriously, my chocolate habit is out of control. I cannot eat it in moderation, so I alternate between my usual diet, containing unbelievable amounts of chocolate (about 12 months) and going completely chocolate-free (about 6 months). That means my weight does yoyo up and down, but I accept this within a range that means once my BMI tips to an unhealthy weight I know it is time to quit chocolate.
I am also very afraid of hunger (legacy of my anorexic years) so I eat lots of nuts, apples and porridge, and allow myself snacks if I need them.
I don't like cooking at the best of times. When dieting, I find it agonisingly difficult to have to be thinking about and dealing with food all the time. When I'm hungry, I find it hard to make good choices. So I stick with a very limited repertoire of easy fast food: omelettes, wholegrain bagels, soup, porridge, baked potatoes... Others would find the lack of variety a real problem, but I'll happily endure a boring diet forever so long as it's comforting, filling and doesn't make me spend time in the kitchen.
Having said all that, I do not have experience of losing the amount of weight that you are talking about. It will take a long time and you want to be sure you get the support you need to get through the long haul. I've never been to Weight Watchers but they do have a very good track record and the evidence of their effectiveness is pretty good. Why not give them a go?