rei, I haven't listened to every song from Hakos Baelz's new album yet, but La Roja is amazing.
https://www.youtube.com/watch?v=ohMBQsgkKMk
That's going on repeat alongside her Psycho, Drown and Boom. And her Identity with Towa if we count covers too. Bae might just be my favorite, music-wise, from HoloEN. I don't know about overall (if we include the Japanese and Indonesian branches Hololive members), but she's a contender for me, for sure.