Brienne would be perfect if she wasn’t a variant of Brint and was her own, independent person that was still as well-done as Brint. Brint is great and is the only one of all the characters that a) has a significant, engaging presence and b) doesn’t have a grating drawback. Atugia is (b) but, as others have pointed out, not (a), which is unfortunate. Those two make for the best companions, conversation-wise. I haven’t really tried Azyrran (she’s new enough that isn’t even listed as a companion yet on the wiki), though her initial conversations seem fine. Nearly everything involving kitsune in this game is what I don’t want to experience in media, up to including having positive relationships with creatures that, in other media, I would gladly see come to harm or brought low, so Kiyoko is out.
Cait has a ton of text, but is basically (a), with none of that text bringing her further than fetish fuel for some. It’s bizarre because she has a better motivation than the PC for everything done; I thought, in fact, that the plan would be to make Cait the primary quest-arranger, sending the PC here and there to further the main plot even when she sat at the Inn all day. (Having her manage Team PC would be a good reason for her to sit out of the party!) Being able to park her in the Inn without consequences broke a bit of immersion, which, ironically enough, was more bearable so long as she stayed parked in the Inn. I’d forgotten about her sister, which helps. Note: it’s possible that she has sex scenes that I wouldn’t dislike, but because I started playing this game early in its development before that stuff was written, parking her at the Inn happens early in my play and I don’t notice I’m missing anything.
Some characters will represent a fetish or two that I like, then have all of it ruined by an overwhelmingly (suite of) bad personality trait(s) that obliviates it, Kiyoko being the best example. (Actually Kiyoko is worse, since there’s the horrible personality and the “I’ll tell you what you’re thinking” writing that plagues the content. Such tendencies are in other content as well, but it’s egregious with Kiyoko.)
Etheryn presents a series of fetishes that I’m forced to engage in, without warning within that subplot, just to make the character mechanically work. That would be a resounding “hell no” before we got to the other substantive stuff that turned me right on off. Because the game had been good with this sort of thing before, I actually thought Etheryn was bugged until I checked the wiki.
I value mechanically-interesting characters, though, and on that scale I go with Atugia and Arona. Arona’s personality is not engaging to me as literally every trope that goes into her is bad imo. If I could turn off her commentary (or, even better, replace it with Atugia’s!) I would. But mechanically, they present a bunch of team-boosting options which work well together even though they’re variants of the same job — melee fighter. Quint presents some interesting combat options as well, but I’d have to use a completely different setup for my PC to utilize him properly and I haven’t had the time to experiment with that yet.
Though not many of the companions are my cup of tea, there are a lot of NPCs that read well to me. If Vaush and Hretha were companions, there’s a risk I’d use them even if it didn’t make mechanical sense, despite my love of combat synergy. Unlike with the kitsune, the bad orc stuff isn’t as universal for the orcs.