I would have chosen USPS, but I currently live in a town without home delivery and I've had many things dissappear from the mail in Flint, MI, so I drive to Lake Orion, MI to avoid anything being processed in Flint.
I prefer UPS as they seem to be the most consistant, and don't have 5 million parts that don't interact like FedEx.
I also like DHL, but it is hard to find places to ship with them.
TEG