Nope, they're all just fine, perfectly edible. Some of the ornamental sunflowers have seeds that are so tiny it wouldn't be worth the effort, but even these are technically edible. Anything which grew from birdseed is a variety selected for edible seeds, anyway. Aside from birdseed use, the "black oilseed" type of sunflower seed is the kind grown to make sunflower seed oil for cooking. The white and black striped seeds, which are larger, are the kind grown for sunflower seeds to eat, since the kernels are larger as well.