I don't have side by side photos or anything, but I do have both of these guys sitting on my desk....so I'll take a shot at it.
The two of them are almost identical in terms of girth, and if you stretch the Adam out (unbend him) he's slightly longer. Mark is 6" total in insertable length, where Adam's full length is 6.75". Adam also has a slightly longer and more pronounced head shape.
I suppose much might depend on how they are to be used. Due to the extra length, Adam tends to be more popular for harness use, plus as you noticed, there's that G-spot curve. Mark is definitely more popular for anal, especially for folks new to that experience.
I hope that helps you make your decision!