For flatheads or blues use live bait, caught a 53lb. flathead a few years ago on a 2lb. channel. Channel cats will eat about anything, live or dead, so chicken livers or stink baits are okay. Common practice to turn a small cat on the troutline hook to use as bait for flatheads, also use goldfish, long lived on a hook , and bluegill.
If you want BIG cats, then you want to go for flatheads. And flatheads like live bait. (blue gill, minnows, etc.) My friends and I caught a 51 pounder on a trot line Memorial weekend. We had shrimp on all 25 hooks. When we pulled in the big one, we were suprised it bit on shrimp, then we found out that a 2lb channel cat was on that shrimp, and the flatty ate the channel cat.
Up north leopard frogs were the absolute best for big blues and flats. I have used frogs down here as well to better effect than anything else I've tried.
Live bluegill or homemade carp bait always seems to produce good results. Not the stink bait either. Vanilla cake mix, vanilla flavoring, maple flavoring, lake water and oats mixed until it packs together. Sometimes we add corn. I would post pictures but all mine are polaroids or 35 mm in a box somewhere.