At least when it comes to the Post Office vs. UPS.
I have never had anything but problems when I get deliveries from UPS. Conversely, the post office has never lost anything of mine and seems to deliver things roughly when you'd expect them to.
Case in point:
I ordered two things from the War Store (online gaming company). One order on Sunday, 10/28, the other on Sunday, 11/4.
The order I placed 10/28 was shipped on 10/29 by UPS. It still isn't here.
The order I placed 11/4 was shipped on 11/5 by the post office. It got here today.
Fuck UPS!