What is the difference between sweet marjoram vs. wild marjoram? The latter - wild marjoram - is actually what we call oregano in the United States. Its botanical name, Origanum vulgare, translates to "joy of the mountains" in the Greek language, since it can be found growing wild along the Mediterranean mountains.
When we think of marjoram, what we are referencing instead is Origanum majorana, which is a different species. Both marjoram and sweet marjoram are the same thing.
As is the case with almost all herbs and spices, the fresh version of marjoram leaves will have a lower ORAC. This is merely because the fresh contains a large amount of water and hence, the concentration of antioxidants (and all nutrients) in them will be less when compared using equal weight.
Research Support, Non-U.S. Gov't: Carlsen MH, Halvorsen BL, Holte K, et al. Nutrition Journal NIH Jan 2010