I've shipped many heads via FedEx Ground. I stopped using everyone else years ago.
Having said that, I used to work in a truck loading hub (UPS) and know that in all of these operations... stuff often gets thrown around. It's simply about the whole speed of the operation and how much freight must be unloaded, sorted, and reloaded at every major shipping hub in the chain. That's gonna create wear and tear. So I always pack my amps with that rough treatment in mind. Amps generally get wrapped in multiple layers of [large] bubble wrap, and that gets put inside a very heavy cardboard box lined with 1 1/2"+ sheets of styrofoam. Tight bubblewrap is the key. Wrap that around the head tightly with 2-3+ layers of bubble wrap that that'll prevent a lot of damage.