Luna : "DOMINATED! Hahahahahaha." "I'll notify yer next o' quee... that ya sucked!" "Hey, Royal Haircut... I might o' taken a bit too much off... YOUR HEAD!" "Mother o' mercy! Now THAT is a bloody domination!" "Lot o' good that royal trainin' did ya! "
I actually think they are equal. Remember that Celestia needed the elements of harmony to banish Nightmare Moon to the moon, not by her own powers.
So, now that I think about it. The whole thing ''Celestia will send you to the moon'' is quite a lot of gibberish when she no longer can as she no longer are able to utilize the elements of harmony.
If anybrony ask me; ''Luna or Celestia?'' I instantly say Celestia. This is because they way I take it is more a question of ''Good vs Evil''
If they would reformulate the question to; ''Who do you like more as a character? Celestia or Luna?'' I'd say Luna because she has a lot more interresting character.
Or maybe I'm not fair there. Luna have had an entire episode focused on her while Celestia has not. If Celestia would have an episode of her own without the episode being anything booring like how a day of her normal routines as a ruler would be, a lot more people would probably prefer her over Luna. That's the way I see it.