I love Lunala! I tend to prefer moon themes to sun themes in general, and I adore all of the bat Pokémon, so I was really excited for a legendary ghostly galaxy bat. I’ve never disliked Solgaleo or anything, but Lunala is just way cooler imo.
Solgaleo is my favorite member of this trio. I like lion-esque Pokemon, so it's no surprise. Lunala looks quite interesting as well, but Necrozma is the black sheep of this trio, in my opinion at least.
Lunala, it is so elegant and majestic, has an amazing signature Ability in Shadow Shield, and is a much cooler Psychic/Ghost-type than Hoopa-Confined. Solgaleo is decent, but its colour scheme leaves something to be desired, and I somewhat like Ultra Necrozma, but really dislike the rest of its Formes.