A few years ago, it would have been Ayu. I genuinely loved all of her songs back then. Now I really only like most of them, love a few of them, and there are some that I don't like at all... x_x
Right now though I think ONE OK ROCK is the most perfect band that has ever existed. <3 I freaking LOVE everything by them except two of their songs. They're just epicamazing.
I think w-inds. are pretty perfect too. Even though I don't like all of their songs, I can't say they need to
improve on anything. They're perfect the way they are.