http://specialist.oricon.co.jp/news/20080829_02.html
This is a survey done by Oricon regarding the best Japanese female artist .
RANKING
1. Ayumi Hamasaki
2. Utada Hikaru
3. ayaka
4. Namie Amuro
5. YUI
6. Koda Kumi
7. aiko
8. Ringo Shiina
9. Superfly
10. BoA
Among Male Voters:
1. Ayumi Hamasaki
2. Utada Hikaru
3. ayaka
4. YUI
5. Namie Amuro
6. Koda Kumi
7. Ai Otsuka
8. Nana Mizuki
9. Ringo Shiina
10. Kaori Mochida (from Every Little Thing)
Among Female Voters:
1. Ayumi Hamasaki
2. Utada Hikaru
3. Namie Amuro
4. ayaka
5. Koda Kumi
6. YUI
7. aiko
8. Ringo Shiina
9. BoA
10. Superfly
ayumi practically nailed it !