Recommended Carrier for Speaker Shipments

So, packagingis more imortant than the carrier.
As to the latter, you are dependent on human factors. No guarantees here, then ....

One last note. There are UP arrows available that will show if the crate or package was tipped or toppled over.
They have colored crystals inside and if tipped the crystals stick to a stickey arrow inside.
They are used on shipping crates for large machines that are shipped by common carrier.
Try Grainger.
Also PACK YOURSELF AND DOUBLE BOX OR CRATE with enough packing material. I usually pack as if I were the one receiving it.

Roadway handled a pair of Thiel 3.6s very nicely from L.A to L.A (Louisville area)...charge extra for residential delivery. One box was slightly smashed, but speaker was just fine due to excellent packing, etc.