Here is one of the two I keep filled... This has thistle seed in it. The other one has sunflower bits in it with suet holders on each side. Each group has stated their preference. The Goldfinches and the Pine Siskens (!) prefer this one. The Chickadees and Bluejays prefer the other one that hangs in the carport.
I enjoy them and I never begrudge the money spent on birdfood!