Quoted By:
Hololive
-- girls are hired for their talent. Don't know each other, or work well together. Very weak group dynamics.
Nijisanij
-- The girls were all indies together going back for years. Mysta, Pomu, Elira, Millie, Finana, Rosemi.....etc all streamed together way before joining Nijisanji. In particular, Pomu and Millie were very beloved by their fans who supported them through rough times. Therefore they have very strong group dynamics, and are genuinely friends together. Watching their collab streams is a pleasure, the natural way they talk and laugh with each other. It feels like you're among old friends.
The girls in hololive are technically more talented (uhh except the council)
But the girls in Nijisanji have something they don't, genuine freindship.