'kay, since so many people are asking me my opinion on who is the strongest captain in BLEACH, this is what i think ( based on up to vol.26)

in order:

Zaraki Kenpachi

Sousuke Aizen

Shigekuni Genryusai Yamamoto

Byakuya Kuchiki

Jushiro Ukitake

Shunsui Kyoraku

Toushirou Hitsugaya

Gin Ichimaru/ Sajinn Komamura (tied)

Mayuri Kurotsuchi/ Kaname Tousen/ Soi Fon (tied)

Retsu Unohana