Well, there really is no absolute "best" carp bait because any bait that's used long enough in a body of water tends to lose it's effectiveness. The fish eventually will grow wary of it, or they see it so often that your bait will no longer be as noticeable to them anymore. One strategy is simply to use any proven carp bait that looks and tastes radically different than what everyone else is using, so that it stands out to the fish. If, for instance, everybody else has been using bread balls for bait, then it may be a good idea to switch to something else like corn, cornmeal dough, or chunks of meat (i.e. chicken livers, hot dogs, bacon, etc.). Strong colors and sweet or spicy flavors/scents also improve your likelihood of a strike, so whatever you use for your carp bait, make sure it gives off a strong taste and that it's a bright easily-visible color (which can be achieved by mixing vegetable dye into the recipe). Carp have been known to go for strong flavors such as vanilla extract, anise extract, curry, garlic, and others.
But for catfish there is this bait called secret seven catfish dip. the secret seven catfish bait is only online so look it up. it is a great bait for catching catfish and you should try it.
I'm not much good for carp fishing, I've never done it. I've always heard that dough balls worked ok, as well as lots of earth worms on a hook. Not really sure.
As for catfish, it really depends on the size that youre going after. Alot of people make poor assumptions that the stinkier the better. That isn't true. A native, smaller fish is the best catfish bait. Bream, shiner, and suckers make great catfish bait. My preference is sucker. Legally, you can only use bait that you've caught in that water system. For example, you can't catch your bait at a pond and take it to a river, or vice-versa, in most states. For smaller catfish, crickets do fairly well as does cut bait. Cut-bait can consist of cut up pieces of fish, or something like chicken livers. I've actually landed some big fish on chicken livers soaked in blue kool-aid powder... and I have no idea why it works... Also, hot dogs do fairly well for smaller catfish...
Good luck...