On mobile so this is probably gonna be a bit short. Oh man, where to start… Almost all of Umineko’s characters are so richly defined, it’s kinda hard to pick favourites like that.
Having said that, first place for me easily goes to Beato. (by which I mean Yasu - spoiler thread or not, I don’t want to leave something as big as her untagged) I love everything about her, from how compassionate and caring she is (even towards the people who’ve hurt her), to her sense of imagination and creativity, to her trickster-y streak and her love of pranks. She’s so wonderfully complex, so human, even down to how she’s “introduced” to the readers through her different faces - while Umineko was plenty special on its own before I “saw” her, I’m not exaggerating when I say that Yasu’s “introduction” was what propelled it from an already fantastic story to something truly wonderful. I could probably go on for hours about how much I love her, but for the sake of brevity (if you can call it that) I’ll leave it at that for now.
In terms of other characters… Man, it’s really hard to say. Battler, Ange, Natsuhi, Eva, Kyrie, Krauss, Maria… Even Rosa, as terrible as she is, they’re all just such great characters. Ranking them is haaard.