Help - cambridge vs. lighterlife vs. slimfast

I'm failing miserably at doing it just by dieting so need something to focus on - I just don't know which is best. I have about 1.5 to 2 stone to lose and want to do it quicky - yes I know but!

So any input would be great. Although I've left two messages already with Lighterlife counsellors so not that impressed already.