in hololive, it's suisei no contest. gura is best of EN and moona is best of ID. i think moona's voice is more powerful, but gura has more clarity and control, and if she practiced more she's easy second best.
but again, suisei is probably best of all, even comparing to toko or chima (who needs a better mic for me to actually evaluate her voice). she regularly tackles extremely difficult songs, just check out her sheena ringo utawaku
https://www.youtube.com/watch?v=OsocHv-2IJc 
