I'll go for the top boy groups' fandoms since theirs are the biggest, as well as me being a bg stan, and it's easier for me to know more about them without being a part of the fandom. This is based on what I have seen on my social media timeline and/or I have mostly interacted with.
ARMYs: I honestly don't know why, but I have seen a lot of stuff about them regarding charity and donations. I have also seen a lot funny memes and clips of BTS on my Twitter timeline. They have two sides tbh. They're like an adult who gives back to others, but they also have a very childish side that likes to goof around.
EXOL-s: I have seen more retweets about them being matured, discussions like an adult would have instead. Can't really explain it very well. They give me 'cool uncle vibes' but in a bit of a sophisticated way.
Additional
Monbebes: I think this is the fandom that I have mostly interacted with, aside from my own fandom, back when I first started stanning SVT. I had a lot of fun tbh, they're very friendly and funny. Had a hilarious and memorable encounter with one of them on Twitter, we talked for hours about SVT and MX interactions as well as random stuff. Haha. Their fandom gives me best friend/soulmate vibe.