Roca is imo the singing powerhouse of idol. Yuko has some songs she does really well with, Rin killed it with Golden Age, but Roca has consistently put on some quality performances.
I think Runie is showing herself to be a big part of Phase's expansion into music stuff, if she isn't already planned for it fishman is nuts because she has a killer voice. Muyu also puts on a hell of a show, I really like this trend where the smaller corpos are starting to get some quality music out.