jungkook. he's not the main vocalist for nothing. jimin is also really good, but something i noticed when i was really into them was that he tends to strain his vocals a lot, like, on high notes. it's not super clean, and it sounds like it's hurting him (i don't hear it as much in their newer stuff, but i also don't keep up w them as closely). but i can't hear as much of that in jungkook's voice.
disclaimer: i'm still learning abt the technicality of vocals/music, so don't quote me, and pls correct me if i'm wrong /srs