FWIW I would never trust USPS to deliver on time in my city. They regularly lose packages for a week or two before magically delivering them, with tracking information that is the long-form equivalent of ¯\_(ツ)_/¯. UPS, FedEx, and Amazon have all been vastly more reliable than USPS. However, USPS has been fine for me in other cities. Maybe, like real estate and cell phone coverage, location matters when it comes to package delivery.

BTW, when you say, "the buy has no recourse other than a refund if shipping takes longer than it's supposed to", do you imply that shipping via USPS gives you some other, more useful recourse if your shipping takes longer than it's supposed to? I cannot fathom what that would be, unless they're going to, like, refund your shipping and then give you $50 or something.

(Actually, if USPS was going to give me $50 every time they fumbled a package, I would ship everything USPS, always. I would order things I don't need, one shipment at a time. I would retire by the end of next year on my earnings.)