I have only had one gun shipped to me by USPS. This gun took 18 days to travel about 1500 miles and arrived damaged. The most frustrating part was that USPS apparently had no way to tell where the gun was at any point during its travels. I find that unfathomable, and since then have only used Fedex whenever I have a choice.
I would recomend USPS registered mail. For most guns it is cheaper to send registered mail (which includes insurance) than to insure regular mail. Registered mail gets sealed and stamped and then each postal employee that touches it signs for it. At each point along the way there is a single employee who is individually responsible for the package. The system if individual accountability is why someone who sends and receives the amount of guns Ken does can go 8 years without a single problem...
If the gun had been sent registered mail ($21 last time I shipped a gun) there is no way that it would take 18 days, and they would know exactly where it is at each point.