The best campground I have ever found was Ocean Wood in Birch Harbor (right near the exit from Schoodic Point loop road). That is quite a way north of what most people think of as Acadia NP, but I think it is worth the drive and schoodic point is well worth seeing. It is right on the waterfront and the owner does not allow radios, partying or other noise which is my primary complaint about campgrounds.

PS - Black Mountain in the nearby Donnell Pond Public Reserve has remote campsites, a great view of the Park and a Cache on top.