This is a post I got from the GAPS forum on yahoo. it explains the diets well:
"I was on Bee's diet for less than a year. I think it is fine to starve off some bugs, but it does not have emphasis on healing foods like GAPs does. IMO, GAPs just takes things to another level. It is the broths and fats and ferments and easily digested, nourishing foods that we all really need to not only starve off pathogens but also feed our bodies. I also do not buy into Bee's idea that we "make our own" probiotics. That is ridiculous to me on many levels. At birth, babies must get their gut flora from the birth canal and from their mother's breastmilk. They do not "make" thier own flora. If they are not breastfed and born by c section, they are born compromised already. Bee's diet also does not have an intro phase for those with severe digestive issues like GAPs does. I could not begin to digest most of the foods Bee's diet may have you eating from the start like steak and salad. Gaps moves you through the diet and phases as you tolerate the foods, and you know when you are ready for something more advanced for your digestion. However, I know there are several folks there who have had success on the diet.
I have not done SCD, but others here have and may chime in too. It is very similar to GAPs, but I believe GAPs is a little more specialized. GAPs is kind of like SCD with additional emphasis on healing foods, a few supplements and detox strategies.
I would chose whichever diet speaks to you and go from there. There are several people here who do GAPs but leave out the illegal Bee's foods and call it anti candida GAPs. Dr N says for most this is not necessary, but that is always an option too. "