A hopper feeder will attract the most variety of feeder birds, according to The Cornell Lab of Ornithology. A hopper feeder is basically a box-shaped bin that dispenses seed onto a tray. It will attract the same species as a tube feeder plus several additional species. A platform feeder set several feet off the ground will attract many of the same species as hopper feeders, according to Emma Willcox and her colleagues at the University of Florida.
Specialty feeders may not attract a greater variety of birds, but they can attract birds you might not otherwise see. Specialty feeders include tube, niger (nyjer), suet, nectar and fruit feeders. A tube feeder, for example, allows smaller birds like goldfinches and chickadees to feed without competition from larger birds. Other feeders, like fruit and suet feeders, will attract birds that regular bird feeders do not. For example, eastern bluebirds are only attracted to fruit feeders, while warblers and wrens are only attracted to suet feeders.
A feeder filled with the wrong type of food won't attract birds. Most songbirds are attracted to black oil sunflower seeds. Black oil seeds have thinner shells than striped sunflower seeds, making them easier for birds to crack open. If you don't want to deal with the shells, sunflower kernels or hearts are a good alternative. Platform, hopper and tube feeders are all capable of holding sunflower seeds.
If you want to attract the most birds to your yard, use several different bird feeders, recommends The Cornell Lab of Ornithology. Multiple feeders can help avoid feeder congestion and prevent larger birds from bullying smaller ones. Fill each feeder with a different type of food and place them at different heights.