I’ll start!
Vocaloid: Flower v4. I love her growls
SynthV: Kasane Teto. I may be very biased here, but I really like her original songs.
CeVIO: RIME. Her breathy voice is cool, and is used especially well in Utsu-P’s collage.
Utau: Anna Nyui. A lot of options, and a pretty versatile voicebank I love to use.
I totally get it! One of the songs I really like was made with a voicebank that is similar to Defoko’s (Adachi Rei) and although I don’t usually like voicebanks like that, the production really made me appreciate it more: https://youtu.be/1G4bYPl09Zo?si=uPzd4yormh2NjU01