Okie Dokie Loki! Here are my reasons for liking Luna more then Celestia!
1.When Twilight and her friends used the Elements against Nightmare Moon they had little to no idea how to use them so they must have used they're default settings. But when Celestia used them against her she banished her to the moon for 1000 years(And that in itself seems kinda harsh) which means she must have had a concuss thought to banish her to the moon.
2.Celestia does not make friends with the 'common' pony. One may argue that she tries but I think she doesn't try hard enough. See, the ponies are afraid of her and she doesn't do much to make them less afraid. But the ponies are even more afraid of Luna and what does she do? She tries even harder to befriend them. And she succeeds.
3.To me, Luna had a pretty valid reason to be upset. I mean pretend you have a older sister who everyone likes, and you're in her shadow even though you are just as good, and nice and beautiful and some may even argue better(I will explain that in number 4). But Every one ignores you. How would you feel? Pretty upset right?
4. The night. I just like the night better then the day. I mean the day sky is kinda boring. What is there? A sun that burns your eyes if you try to look at it? A bunch of fluffy clouds? A plain old boring light blue sky? And then there is the night. Which has thousands of beautiful shining stars and some planets. A moon that you can gaze upon without fear of eye damage. You can't see auroras during the day. You get sun burned during the day. A grey cloud during the day is ugly but at night with the moon it's beautiful. The only thing the sun is good for when it comes to navigation is telling you which way is East, West, North, and South. But pretend you wake up in the middle of the day is the sun gonna help you if you don't know whether it's AM or PM? Nope. But the stars are consent and have helped sailors navigate for centuries, and the north star never moves.
5.Luna watches over dreams so if somepony has a nightmare she can help console them. Can Celestia do that? I think not!
6. What happens to the moon when Luna is banished? Celestia takes over, which meas that Luna was never really needed, that she was useless, that her special talent had no meaning. Kinda like Flutters during the Grand Galloping Gala, but no one made to big a deal out of that except some gossip. I mean their situations where pretty much the same. Their special talents were useless and ignored but when Luna takes a stand she's banished to the moon. When Flutters takes a stand she causes some gossip and chaos but no long standing effects, not even a bill!(I love Fluttershy don't misunderstand me)
7. Celestia traps Dicord in stone but what is he set free by...Three arguing fillies...Seriously Celestia? Really?
8.Celestia traps nightmare moon in the moon for 1000 years. She's your sister Celestia! You couldn't trap her for 100? Her hatred probably grew even more during those years! And when she is released is there any effect? No, there is no effect. So why couldn't she be banished for 100 years? Surely there would be other ponies to bear the Elements of Harmony!
9. Where was Celestia during the Summer Sun Celebration!? Did Nightmare Moon imprison her? But then why did she just walk in at the end of part 2? Was she just sitting on her plot letting Twilight and her friends take care of it? Also why did she send Twilight and her friends to defeat the dragon in dragonshy? They almost died! And they would have had Flutters not given the stare! I mean she is one of the most powerful ponies in existence she couldn't flown over and done it!?
And those are my opinions! Sorry if you don't like them! Also sorry for the wall of text!
Oh! And also! I don't hate Celestia and I don't think the sun is useless or anything! I just prefer and like Luna better. Also, I haven't really seen any of the Celestia memes so those haven't influenced and opinion.