I have the Moss 4 skim and have ridden the 2012 Keenen. As stated above, the Keenen is the same shape as the Moss, but lighter with sharper rails. Overall this makes the board feel faster and more lively. It also seems to spin fast possibly due to the slicker carbon fiber.
You could always grind down the rails on the moss to your liking a la - Jeff Walker. (http://flyboywakesurf.com/hot-rodn-the-ooze
I really enjoy the skim style boards, I'm currently on a Phase 5 Drew from 3 years ago. The size fits my body profile 6'1" and 190lbs better.