I've watched a lot of idol and music animes but it really has to be Hatsune Miku. There are more classic idols, there are idols with more character, but I think Miku embodies idolness with absolute purity. That's all that defines her, she is everyone's idol and anyone can sing with her voice. For the sake of the performance she can become anything. She is music and dancing personified. She is also a digital goddess who can be worshiped forever, instead of having a few years in the sun. All that takes away from this is you can't shake her hand after the concert.
>inb4 she's not an anime character
Yes she is