Which brand of cocoa powder is the best to use?

I have a chocolate cake I make from scratch a lot. The only thing that really bugs me is when I use Hershey's cocoa powder it always creates these little in my batter. I know its just the cocoa b/c I've smashed it before to see. I even thought the powder was bad & used a brand new can and had the same problem. I ALWAYS sift my dry ingredients right before I make this cake so I'm thinking its got to be the Hershey's cocoa powder. Has anyone had a problem with like this? Can you recommend another cocoa powder that's better? The stores close to me only sell this brand so I don't know of any others.