However, Captain Toushiro is said to be a very strong and intelligent captain. Kyoraku himself (now the Cpt. Commander) commented that in about 100 years Toushiro would certainly have surpassed him. that coupled with the strongest ice zanpakuto (pre bankai rukia) and enough intelligence to make effective use of it and fighting a water type resurreçiòn (giving him more then enough water or moisture to active his abilities) he was as much at full power as we could have seen him. And she still almost beat him, despite his advantage in matchup.

That said, I'd peg my choices for war potentials as follows: Ichigo (confirmed), Zaraki, Orihime, Aizen and Urahara

Ichigo is confirmed for his template stacking (which by the way explains his shortage of combat maneuvers compared to the rest)
Zaraki because he is a freaking powerhouse, and bit of a wild factor
Orihime because of her ability to Summon: Ichigo
Aizen because of his fairyness
Urahara because of his tactical value: he has a lot of resources (tessai, science items, Yoruichi), vast intellect and knowledges, great fighting and tactical skills and his Summon:solution to any problem flung his way.