Comparing US Postal Service to UPS is not fair. USPS doesn't have all the flexibility that UPS has with regards to price and whom they will service. The US Postal service has to pickup and deliver mail to all Americans, UPS doesn't.
In my experience, Fedex and UPS deliver when they say they will. USPS "attempts" deliver all the time only for the package to fail to arrive. I live in the urban part of a small city/big town. There is essentially never a reason a package can't be delivered.
My latest gripe concerns the USPS person that delivers my daily mail. She loves to catch me outside and let me know that she doesn't "legally" have to deliver my mail if there is snow on my steps. I live in New England. Everyone has fucking snow on their steps.
(Written above the postal HQ in Manhatta)
edit: and they charge more for hard to reach places. really.