Here are two old BG's from a 'Goldilocks and the Three Bears' Short we did for Oxford University Press many years ago. You can see they are the same BG but different. That's because one was the first version that had to be redone as it wasn't quite right and didn't fit with the rest of the BG's. Just looking at the two BG's in isolation there doesn't seem much wrong with either of them. But in fitting in with the rest of the show the top one was incorrect as it was too dark and had too many outlines in it.
I think if I had to choose a stand alone favorite now, I would probably pick the top one.