USPS is one of only two couriers I'll actually select if I get a choice. They put my packages in my mailbox (I realize others legally can't) or if it doesn't fit, they bring the packages to my door and knock. UPS is the other.
Other couriers place packages on my driveway, halfway down my stairs, or in other weird places. Occasionally one of them will actually come all the way down the stairs, but they won't knock.
In the Universal Postal Union’s report for 2018, US ranked #8. Australia ranked #26.
I think it's just anti-government hyperbole to pretend that taking an envelope from your hand to a farm house on the other side of the country for 55 cents and having a line for such an amazing service is too big an ask.
It would take just as long at Fedex or UPS. They're private. They don't mail anything for 55 cents. They're usually more expensive for packages even.
It's really pretty amazing.
Other than that, I've never had a problem except for waiting in line and being served by an intentionally slow employee.
I haven't run a company which ships packages with AusPost, but as someone who receives packages fairly frequently and sends packages occasionally, I've never had any significant issue.
EDIT: I should've said "postage in the US", not USPS. My response was in relation to someone saying that it is "the worst". I've had much worse experiences with private shipping companies like StarTrack.