I think worms are better than feeding fish feeder fish. Most of the feeder fish out there aren't taken care of and would like get more disease than give fish good health. For example, if you have an oscar that has fungal infection and it only eats fish, then you would need to feed him fish, but you don't know how well those feeder fish are taken care of. Your Oscar would more likely to get sick than anything. It's probably different if it's your own batch, like livebearers, or something. I just think it's wrong. I have Grindal Worms and that's what I feed my fish interms of live food. They like 'em. You can also get some bigger worms for bigger fish though.
Over all, most things have been said.