User blog comment:B214/Volume 17 spoilers./@comment-24468758-20140301105227/@comment-1359322-20140301112654

Actually Ishibumi already ranked the girls once in his twitter in the past. It goes:


 * 1) Rias
 * 2) Asia
 * 3) Akeno
 * 4) Koneko
 * 5) Xenovia
 * 6) Irina
 * 7) Rossweisse
 * 8) Ravel
 * 9) Ophis(?)

Of course that was in the past, so there is still a possibility of Ishibumi changing the ranking.