We have clients in Asia who insist on USPS shipping...it is likely easier to get stuff thru the customs/graft maze. Some times the tracking is accurate, but oftentimes packages never "leave" the facility at JFK airport. We never really know if they make it or not without contacting the client.
Most of the others have fairly accurate tracking, but throwing a change of address into the mix can make for an interesting journey.
For international shipments, DHL is awesome. They do not play and will handle anything that they "can get on the airplane" for us along with unlimited insurance coverage.
FedEx, UPS, and USPS have size limits which can give us fits.
I just got a box of outdoor gear via FedEx ground from Black Diamond in Utah(?) that was a 4 day trip and the tracking was accurate.