For big cats, especially flatheads and blues, bluegill.
Here on the James, live bluegill will slay Flatheads in the upper portion of the tidal James.
Downriver, or at least twice a day it's downriver, fully grown Gizzard Shad cut up in big pieces worked for the big blues. I cut a full size shad into 4 pieces and use an 8/0 hook