Since anything of value that I ship I want to have a tracking #, I prefer UPS (no local FedEx shipping point).
My son returned a non-working part to a vendor by mail and was in a tizzy when he contacted the recipient after a week and it had not yet been received and there was no way to track the package. Fortunately it did get there in another couple of days, but he was really sweating it for awhile as he wanted his $50 back for the non usable part.