The 13 are ranked in order of their overall power (although some lower ones can win against higher ones via match-up), and not squad number:
Mayuri can possibly be a lot higher with right prep time. This is just judging his basic combat abilities.
- Genryūsai Yamamoto
- Zaraki Kenpachi
- Hitsugaya Tōshirō (Adult Form)
- Urahara Kisuke
- Shinigami Aizen (Could be higher)
- Shunsui Kyōraku
- Kuchiki Byakuya
- Healthy Ukitake (Assuming he's somewhat close to Kyoraku)
- Kurosaki Isshin
- Tenjirō Kirinji
- Kirio Hikifune
- Retsu Unohana
- Kurotsuchi Mayuri
Hikifune and Tenjiro are featless, but are placed that high because of their portrayal. Tenjiro is above Hikifune as he's older and was promoted much sooner (also has bit more showings, casually blitzing Soi Fon).
Idk if Gin makes it. No idea who I can possibly replace. He might make a case for being above Mayuri in combat, but when prep and other advantages of having him are taken into account, Gin doesn't even come close.