I did Cambridge and lost 6 stone a couple years ago, so found it successful. I ended up getting pregnant and gained it all back, and this time I've decided to try Slim and Save. I've been doing this for 2 weeks and I really prefer the SS food and the fact that I can eat 4 times a day.
I think it's down to your resolve. If you are totally motivated to do this and don't need external motivation to stay on track then SS will work for you. If you feel like talking to someone about your weightloss for over the past week and feel that that would keep you on track then maybe CD is the way to go. I found that it also depended on the counsellor. Talking with someone you get on with can be helpful. If you don't like them it can be trickier.
Good luck, which ever you choose.