Personally, I'm leaning towards wall color, because of the shape of the
room and the placement of the angled portions. The 3D view is what
really did it for me. The angled portions just look like they're part
of the wall, not the ceiling. Painted ceiling color, the would look
weird extending halfway down the wall, particularly in the the narrow
section. The narrower slanted part should definitely be wall color,
otherwise you have a little ceiling colored rectangle in the middle of
an otherwise solid colored wall.

For illustration, here's a photo of a room in a house I manage:

http://houseonhawthorne.com/masterbed.JPG

Granted, this is not exactly the same arrangement, and the moulding
does provide a clear wall-ceiling demarcation (and who knows, maybe
that would be a nice solution for your room). Still, the walls
definitely do not feel like they are falling in on you. Further, if
the narrow section on the left were painted white (even without
moulding), it would look really out of place.

My two cents. Of course, the idea of trying the lighter color then
painting over with the darker sounds pretty good, too, just in case.