actually, proper answer now that i'm awake and have had some time to percolate lol. best thing armand did!
i should say this is kind of a tie for me because the person armand becomes with daniel is always going to be up there -- he didn't let him die, he gave daniel what he wanted, but more importantly he told him, and showed him, that he loved him, and just in general in their time together he allowed daniel to see so much of his real genuine vulnerability and cared for him and worried about him so much and that fucks me up!!
but!! the thing i actually wanted to mention is his homes! (this is maybe cheating a little bit because it isn't something he did, it's something he does, but whatever.) one of the things i love most about armand is that he's always creating these stable places and central points for everybody to congregate on. while a lot of the others are sort of nomadic and don't stay in touch and you don't really know where they are, he is always (as he says) "a canker in the very eye of the world". he's easy to find, he stays in one place and he uses his resources and his power to create these stable, lasting home bases and then opens his doors to others. he creates stability and then shares it in a way that really nobody else does.
and i think it's very interesting because this sort of stability is a character trait that (i think!) maybe most people would first and foremost think to associate with elders like maharet, or marius, when in actual fact, the truth is that neither of them has ever done that -- for their own disparate reasons they've always been highly reclusive, and have protected their own stability by staying out of touch with the rest of the vampire world, not opening their doors, and for the most part not helping anyone or intervening in anything in any way.
there's something fascinating and honestly poignant about like... armand, maybe subconsciously, running a household according to an ideal which (imo!) is based on marius, except that marius has never actually done that. not for vampires. and so in actual fact, this is something that armand has innovated; this actually comes from him, and is coloured by his experience with the covens (which marius has never shown anything but disdain for), and perhaps even beyond that, by his experience with the sense of community in monastic life (which really ditto).
i personally suspect that rather than praiseworthy, he probably sees this as ultimately pretty self-serving on his own part, because he has this longing for community that drives him to create these places, so he probably just sees it as something he does so that he won't have to be alone. and also, from the way he talks in late canon you get the sense that he rather sees himself as trying to atone, and as trying to emulate those who are better than him. when in fact he's doing something that nobody else is doing, and in many ways (imo) behaving more like a leader of a community than any of the characters that everyone else thinks ought to lead, like marius or lestat. not because they couldn't, but because neither of them has ever had the resources, capabilities, patience, and willingness to create something like that and then open it up.
and for a character who's been so lost, and has spent so much of his life feeling lost, feeling abandoned (and i think, right up until present day, still feels that way really), and has spent so much of his life looking for something to anchor his life to, without ever having the luxury of truly finding it, and having to just sort of go on anyway, keep living anyway -- for that character to be a stable anchor point for everybody else is something that really really gets me about him, maybe especially because i think he isn't fully aware of it himself.