I do a lot of shipping for the aluminum parts I produce and sell to fellow robot builders.
Here in the United States, the US Postal Service offers flat-rate services for certain box sizes ("If it fits, it ships") but there is also limited tracking. But that's from here.
Receiving from other countries, such as Ultimaker or when I contract out the fabrication of a part to Europe or Asia, DHL has proven over and over again to be the best. Cheaper than FedEx and UPS most times, I have never had a DHL shipment go missing or get damaged.
So while I may not always like the costs of shipping...DHL has always done right for me