They do a good job with my packages, but I find that tracking is hit-and-miss. A lot of packages don't show up in the system until they are delivered.

I ordered coins from the U.S. Mint and, because of the value, I was upgraded to priority mail at no added charge. Priority Mail takes 2 to 3 days to go across the country. But the U.S. Mint doesn't actually use their own federal post office - they use FedEx. FedEx takes a week or more to deliver the same package, in large part because FedEx does not move packages during weekends. It took 8 days to get my "priority" package.