I have good success with black oil sunflower seed. And if you slap a suet holder on either end of the feeder, suet is a popular item during nesting season.
If you get the store-bought suet, make sure you get the kind that's good at higher temps since the stuff meant for winter use will melt when you get close to 80 degrees.
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."