It's a tie. You can't make me choose between these two:

Moneti is the first. Not only did they do my rainbow waifu Red Ginger, but they also did one of my other favorite rainbows Red Spider Lily. I've also seen Hollyhock on other teams and she looks amazing! Definitely a rainbow that has caught my attention that Moneti also did. Some of my favorite golds that I left behind on Nutaku were also by them like Dahlia or the one 5* I always wanted but could never manage to get Nandina.

Utsurogi Akira is the second. I was fortunate enough to get Maple on Nutaku through a priority gacha and she just WRECKED everything. Queen of the Night was one of my favorite and cherished 5* I got through gacha (hope to get her back soon) and I really enjoyed Canna's design among a majority of the event girls while on Nutaku. And I've always wanted Apple of Sodom, Gardenia, and Night Phlox.

So yeah, those two. It also helps that the both of them tend to favor OPPAI!!!!!