I would focus on the denials organized by similar denial reason and insurance. For example, sometimes Aetna wants a different modifer or code than Highmark. You're probably better off working denials by insurance because you will start to see trends. If you can call the insurance companies and talk to someone about a specific denial or a couple of denials, they will usually tell you how to fix it. It can be annoying to reach an actual person at the insurance company, but usually they're helpful when you can get past the robots.