I have to say I've been really lucky with both UPS and USPS. I still favor USPS, though, because the few times something went wrong, it was made right quickly.
We picked up a new mail carrier who was not as hard working as her predecessor. I had to pick up some medicine from the PO because she left a note about attempted delivery and nobody home. We were home however. Several weeks later I was expecting a bow, so was watching for her. She whipped up to our roadside mailbox, slipped an already completed "attempted delivery" notice in the box and was gone before I could even get out the door. I took the slip to the post office and talked to the manager. I explained that this was the second time it had happened. He copied the slip and said he would talk with her. The next day I picked up my bow and nothing more was said. The mail carrier will now get out of her truck and ring the bell if she has something which needs to be signed for and I tell her how much I appreciate it. Every business has employees who do not even go the mile, let alone an extra mile, but it is how the manager handles the problem that makes the difference. So far, I'm very satisfied.