Same here! My favorite JP cover artist is definitely Yuu Miyashita. His voice is so flexible, and covers some fantastic songs. His cover for the song Wozwald became so much more popular than the original, that it pretty much became the definitive version and was remastered and released to Spotify!
Aside from cover artists, the first JP Youtuber I subscribed to was 岩下スティーブン, whose channel is largely dedicated to reviewing action figures. He’s become so much more confident in front of the camera since when I first started watching!
I also really like 2BRO, which is a gaming channel. Although they largely play horror games, they play a few others too. I find that the main player, Otojya, has a very nice voice to listen to, even though he speaks quite fast. It’s good practice!
There are a few others, but I mainly watch those three.
Edit: None of those were VTubers, but I wasn’t sure if you meant favorite JP Youtubers in general or only VTubers…