I'm very skeptical about 5:2 (some good info
here), as well as Atkins. Short term though, unless you've got health problems, any diet which means less calories in than out works and is safe.
I've tried the Dukan diet in the past, with good results (also a high protein diet, but less extreme). Decent site
here.
As for training, few things speed up weight loss like a combo of brisk walks and some weight lifting.