It's an interesting question, because there are VERY active fandoms that just don't have a large number of people on KPS who are part of the fandom, and there are fandoms where I know there are a LOT of people on the forum who are at least positive, want to see them do well, etc. toward groups, but there doesn't tend to be a ton of news brought here or lots of comments on their updates (like Xdinary Heroes). And of course, high profile releases or news get a lot of buzz, even just in a "as a person into Kpop, I'm mildly curious about this" so that's not necessarily representative of those highly commented posts actually representing a lot of fans.
If I had to guess on what gets the best balance of lots of people here stan the artist AND make a point to comment on posts/bring news here about them, I'd put my money on...
- Girl Group: DIVE - IVE
- Boy Group: STAY - Stray Kids
- Soloist: Jigumi - Yena
I maybe overthought this.
