(for length purposes i will limit myself to the main trio hahaha)

harry - from what i remember about harry he seems to work best with people who are more extroverted than he is, but not too annoying or unpredictable(tsurumaru) so someone friendly but not overbearing, like mutsunokami or shishiou! i feel like they can guide him while also letting him call the shots, if that makes sense. mikazuki might also work, but only bc harry is probably the only one who knows best how to interact with weird old wizards lmao

ron - no one too weird, that's for sure. or else he'll probably be complaining about the partner-up the whole time lololol. but ron himself is friendly if he thinks you need a friend, so maybe manba? though i feel like he'll also work well with someone strong and silent, like taroutachi or nenekirimaru. he won't pick a fight with them if he knows theyre way too strong hahahaha

hermione - omg i feel like she'll blend well with almost anybody, but i would personally partner her up with kasen, hasebe, or tomoe, just because she's similar to them. or maybe thats a bad thing...? in that case, perhaps someone who is fun, but wont be too stressful for her, like horikawa!