USPSs tracking sucks. Half the time I get the box before the site says it left the company. But up here, they are the only reasonable way to ship. I have had very few instances of damaged boxes by USPS.
One thing to note about USPS. If you ship Priority, and it is less than 1lb. It will be transported in a commercial passenger plane. So the baggage employees are handling it too. Any mail over 1lb may not be shipped in the cargo hold of a passenger plane. FAA rule. I guess they figure <1lb of C4 can't destroy an airplane.
Also the airlines are charging an additional fee for large boxes. It is now usually cheaper to send two smaller boxes than one large one.