Aizen vs These 4

Kisuke, Yoruichi, Ishin( Ichigo's dad) and Uryu's dad(can't remember his name)

Both sides get 2 weeks prep.

only Yoruichi we have a good showing of, and she has never revealed her Zanpakuto.

Everyone else's abilities are unknown, especially Isshin.

Ryuuken

well i dunno since i havent watched to much(the english dub is up to 47-48) but id say urahara could do alot.

Aizen pretty much set them straight with the Hogyoku.