I will also add in a vote for USPS but you have to go in knowing what the rules are.I like the way Jack (rabbit) does it and it does lessen the chance of "standing in the corner with your packag"I have found this site a while back somewhat dated but still helpful.
http://www.thegunzone.com/ship-guns.html

Shipping of guns,especially when you add in C&R and handguns can be very confusing and open to interpredation but a long gun through the USPS is a slam dunk legal as long as the reciever is a FFL.

Hillary For Prison 2018