(Was gonna say, the Matsudappoiyo, Keine Ron, and Shiine Ama are very popular haha)
Cinnamon Ani Usa - shonen nasal voice is amaze so perf
Waon Ikuto - Dunno if he got more popular? Is also amaze, is unloved becuase he's a furry isn't it
Halt Tanner - Her tripitch VCV is the best mature female UTAU srsly! Heck her
CVVC JP 12-pitch bank (that you might have to ask around for as Cdra isn't really active anymore ;; ) and her
English CVVC are a must also!
Sorane Yui - Everyone knows her sister Rana, but Yui is fantastic too! (Sorry for the middle of a video link, I can't find anyone using her bank well. :/ )
Tomone Mito - Dunno again if he ever got noticed, perfect young guy Kire.
Kion Yura - Her hard bank is the best I've ever heard of Kei-style female strong monopitch
Kuon Kono - shonen voice with a large variety of banks to choose from! I encourage checking out
his tag on NND to find all his voices, he has whispery ones, powerful ones, mellow ones, loads!
I like a lot of super popular banks, it seems like shonen ones aren't as popular though which is why they popped up frequently here. :'D