Is there a single best seed or food type for feeding birds?
It certainly depends on the species but black-oil sunflower is the best over-all choice. It's thin shell makes it popular with the smaller species and many different species will readily be attracted by it.

Goldfinches are especially fond of Nyjer® (thistle) which can be feed in thistle feeders or seed socks. Feeding Nyjer in seed socks often helps discourage house sparrows and starlings.

Cardinals are fond of safflower, a seed also less popular with house sparrows.

Orioles and woodpeckers can be attracted by fruit, such as orange or grapefruit halves.

For photos of various seed types visit the Wild Bird Feeding Industry Web site.

Visit the Birdzilla.com Web site for a seed chart and additional feeding tips and information.