I like the new one that seems to be Nyanners-inspired more than the one she had toward latter part of 2020, mostly because the new one she does a lot of faces that come out looking like derp faces, especially when she collabs with other vtubers and tries to look around. I think it's kinda tricky for her to get the tracking stuff really accurate because she already has shit like oxygen tanks tied to her, so that may be why sometimes it looks like her face sticks like it does.
Edit - rewatching the Mel/Merry/Lumi collab. Holy shit this Euro pair might be my favorite collab I've seen Mel involved with and it started out looking bad because their game got fucked up so it was essentially a multi-hour impromptu chill chat stream. Lumi's high energy, Mel's galaxy brain and Merry's dry humor made it perfect.