In a bowl, mix buttermilk and ranch. Add drumsticks, cover, and chill 2-6 hours.
Preheat oven to 425°F. Line a baking sheet with foil and place a wire rack on top.
Whisk panko, Parmesan, garlic powder, onion powder, paprika, salt, and pepper in a shallow dish.
Drain each drumstick, dip briefly in melted butter or oil, then press into panko mix to coat.
Arrange the drumsticks on the rack and bake for 35 to 40 minutes, turning once, until golden and the thickest part reaches 165°F (74°C) without the thermometer touching bone.