The saddest ending in my opinion was probably Rin's neutral ending followed by Shizune's bad ending. Hanako's bad ending in my opinion is nowhere as near as powerful as people says because I thought it was predictable and easy to see coming and the fact that I've seen similar situations (unjustified in those cases though since it was due to mental issues for these people.) that put this one on a less dramatic level just made it not that effective to me and the fact that the situation has a *certain* chance to be repaired over time just crushes it's effectiveness more to me.
It is pitch black. You are likely to be eaten by a grue. (This topic has been eaten)
Start with Lilly, to make sure you have her bad ending out of the way (you'll understand why when you see it; the structure is a little odd, but it's by far the most commonly missed one for 100% completion). Finish with Hanako's bad ending. Other than that, do them in whatever order you think fits best.
"Playing a game for its graphics is like watching pornography for the story." - Kadiroth