I find it humorous that Princess Luna is so much more popular than her sister among us humans, considering that she turned into Nightmare Moon because she felt overshadowed by Celestia in the pony world. I like to imagine her surprised expression if she ever learned how fanatical we are about her.
If ponies had liked Moonbutt as much as we do, perhaps Celestia would have been the one to feel jealous and turn evil. I wonder how differently things might have turned out. Imagine if Luna had ruled Equestria for a thousand years.