I've done WW both ways and I've always had more success when I attend meetings. Like a pp said, there is just something about the accountability of having someone else weigh me that keeps me on track. I usually really enjoy the meetings too, but it is important to find a leader/meeting that is right for you. I like the leaders who encourage you to make the program your own and find what works the best for you.
Right now, I'm using the Monthly Pass, so I get the advantages of both the meetings and the online tools. I love the online tracker and I was happy that I didn't have to give that up by going back to meetings. However, it is more expensive than just using the online program ($39.95/mo v. $16.95/mo), but to me the meeting is worth the $6 extra each week. It's still a bargain compared to some other weight loss programs.
Good Luck with whatever you decide to do.