I rate Slimming World highly - it is the ideal "diet" if you are greedy like me, because you can eat constantly as long as you are eating the right things!! It also seems easier and less "faffy" than others, cos you just stick to red or green days and only really need to work out your "sins".
I was a member a good ten years ago, and lost 3.5 stone. Unfortunately, when I reached my target weight, I decided I would just follow the plan at home and not attend the classes, because I knew what to do and it would save money. Well, you've guessed it, I didn't stick to it and so I wasn't at my target weight for very long!! I am considering doing the plan again because I have the books and I am capable of sticking to it, I just need to find the willpower. But it's gonna have to be fairly soon as my health is suffering because of my weight.
I recommend that you go to the classes for the motivation. Everyone is really friendly as you're all in the same boat so they all understand. They also help support you and bring recipes etc, so I'd prefer it to an online thing. When I first joined, I was puzzled as to why there were some slim people there - they didn't need to lose weight. It was a while before I realised that they had been overweight but had reached their targets, and were attending to maintain their weight! So that was quite a motivation too! By the way, your weight is always confidential, it's not shouted out to the group and you don't get told off or anything if you don't lose anything!