Iwasato Yuho: She has written many anime theme songs, with many of them sung by Maaya Sakamoto. One example of Iwasato-san's brilliant (yet confusing) lyrics can be seen
here.
My other favortie is Ayumi-- she always has something to say about everything. Like Ayu herself said, her songs are either about love or freedom, but the way she describes something, it has several meanings. She might be talking about a personal experience, but in a way, we can all relate to it.