I am on the record as supporting our USPS as a great organization. All companies/organizations have examples of mistakes or bad service, but the USPS does a great job by far. You cannot beat the Priority Mail FRB/Media product anywhere in the world (free box, free tracking, basic insurance, 3 day delivery in USA, almost unlimited weight if it fits in the box).
Regardless, for international shipments, it is important to understand how the postal systems work. The USPS cannot address/resolve what it does not control. When you order or send something international, the USPS gets it from, or hands it off to, the destination postal service, which may be run like crap. The shipment is beyond the USPS ability to QC at that point.
I have used USPS, UPS, Fedex and DHL extensively for domestic and international for years and each has their sweet spot. Even by specific countries you will find Fedex is better than DHL or vice versa based on their local operations.
If you want a somewhat "guaranteed" quality of service, you need to use a global fedex or dhl service where it is in their hands end to end (I include their foreign subcontractors/partners since they are still within the DHL/Fedex ecosystem and logistics tools). Nothing is free and these companies are not subsidized by their governments, so it will cost more, but take less time, have better tracking, better customer service, and you get "one throat to choke" if you have issues.