What's a good feeder fish?

I've been feeding common gold fishes to my alligator gar this past few days, and I've seen a lot of posts in several forums that those common gold fishes don't make good feeders, so can someone tell me the pros and cons of a feeder gold fish? and can you also suggest some good feeders as well?(except the worms cause he doesn't really like to eat it). Thx a lot