Vocals are gonna be down to genres of Music that people like for the most part, but I'll try to be fair.
I'll say that Aiden Grimshaw, Luke Friend, Leona Lewis, Lauren Platt, Alexandra Burke, Rhydian Roberts, Ruth Lorenzo, Paije Richardson, Hannah Barrett, Seann Miley Moore.
To answer about Max to the OP, I really thought that he had potential, I just feel that he needed to understand his sound a bit more though instead of trying to sing a genre that he likes.
It'd be my best advice to him going forward in Music.