I've used UPS and USPS to ship my coilovers and other larger items. Both of them came with ripped boxes but nothing was damaged.
When I shipped with FedEx, the box came in good condition unlike others. I've shipped a lot with FedEx and seems like every time I receive something, the box was in good condition.
My choice would be FedEx, then USPS and then UPS as the last one, since every time I receive a package, the box is ripped and couple times the item was damaged.