Hmm.. This is quite hard to answer.. Anyway, if I should rank them, then, here we go : 1. Yamamoto Genryuusai Shigekuni [No doubt.. Though he's old, still think he's the strongest] 2. Zaraki Kenpachi [i think he could be stronger than this.. But well, since he couldn't performed Bankai, so he's number 2 that is..] 3. Kuchiki Byakuya [Cuz he's awesome, and that would be it.] 4. Hitsugaya Toushirou [This is pure a subjective answer.. Well, I'm his fans, so I just have to put him here~ But hey, he's young and he's a captain.. A strong one for that.. Don't you think he'll be so much stronger when he's older ?] 5. Kyouraku Shunsui [He's a senior.. I think he just doesn't showed his skills that much so he doesn't looked so strong..] 6. Ichimaru Gin [He's a villain. But he's strong.. And somehow, I have a feeling that he's naughtier than Aizen..] 7. Komamura Sajin [i guess, I'm judging him by his appearance ?] 8. Soi Fong [Her skills were still rather raw from my opinion.. I believe she could be stronger in the future..] 9. Tosen Kaname [Well, I don't have much to say here..] 10. Unohana Retsu [i think she's actually stronger than she looks.. But, dunno, I just can't get the impression of her battling the hard way..] 11. Kurotsuchi Mayuri [He mainly fight with his crazy scientific ways.. He's strong in his own way, but well, he's still, a scientist after all..] 12. Ukitake Juushirou [i believe he's actually much much stronger.. Maybe around Kyouraku's level.. But his unfortunate condition was kinda, unfortunate.. So..]