I recall reading in our local rag some years ago, around 98 or 99 I think it was, that UPS, Fed Ex, and the USPS, all used each other during the holidays. Each had their strong points. The USPS though had the best distribution system in the US at the time and the other two used them extensively during the holidays.
Dunno about now.
The USPS is in the US Constitution though. Currently, they got the worst of both worlds. They are not federally funded, operating as a "private enterprise", but they have to obey the federal government mandates.
My opinion:
Either put them back totally under the government or let them be private.
Personally, I think the USPS does a good job. At least around here. The doggies will let the post office guy in the yard. The UPS and Fed Ex guy, not so much.