The rate of accurate and on time delivery is better at the Post Office than FedEx, and is right there with UPS. Does the Post Office have problems? Yes, but having worked there for 30 years now, I can say that I would want something sent USPS way before I'd send with another carrier. And we probably average 5-6 packages a week in my house, and we may have an issue once a year at most.
I have spent a lot of time tracking down packages for customers and for friends, and it is very rare to have one of those "missing" packages not have a legitimate reason it went missing. Most of them that I have to track end up either having two labels on the box or the barcode is smudged so the scanners can't scan it. The other common problem is when a smaller package gets put in the wrong container at the sorting facility. Instead of going from Knoxville to Louisville, it ends up in Birmingham because it fell in the wrong container.
Yes, I am well acquainted with the lazy sloppy workers, as well as the poorly managed company. But I have been very happy to have now worked here 30 years.