What is the best bait?

The following is just my opinion and I'm not an expert by no stretch of the imagination, but this is what works best for me in the areas I fish the most:
The best way to find the best bait for whatever species your fishin' for is to find out what they're feeding on in that particular season or area. And the most accurate way to do that is when you clean them look in their stomach.
I have found that when nothing seems to be biting, regardless what I throw at 'em, something will always hit on live bait. Catfish love big fat juicy nightcrawlers, not the store bought kind either, the kind you dig yourself. Bass like them, too, but a nice shiny minnow will get their attention before a nightcrawler will. Bass love crawdads too, gotta be the right time of year tho, usually late spring, early summer, when their shells are soft, this is a good opportunity to fool 'em with an artificial lure. Catalpa worms and Cicadas work well, but it has to be the year for them, fish somehow know when its time and won't hit as quick as when their naturally available.
Another artificial bait I like is the 4 inch black rubber worm, have had really good luck with those. Caught my biggest bass ever (7 lbs) with one, floating the river around 1p.m on a very hot August day when nothing, not even perch, was biting. Hope I helped a little.