I would argue that it is about case #2 here because we're talking about 3 forwards. Can anyone make a case that one is better at defense over another? The +/- is subjective to the overall team in a lot of cases, but FO% to me is a big factor for the defensive side because it's an opportunity to directly defend the puck from your opponent. Crosby is known to do this regularly on the Penguins penalty kill. The reason that I didn't put up OV's numbers is because his don't really apply across the board in the same way as the two centers.
eidt: misunderstood your post the first time through. more thinking required.