I really like USPS for everything except large, lightweight packages such as bicycle rims. For domestic shipment of rims or wheels UPS is better because they don't penalize you so much due to the size of the box. I imagine FedEx is good too, but haven't tried them.
I've shipped a number of pairs of rims via UPS Ground over the last few years and never had a problem. I buy and print the shipping label at home through PayPal, and pack the rims myself. For some reason, eBay consistently overestimates the cost of shipping via UPS. I've had to reduce the stated weight or cut back on the handling charge to get the total to come out right. On the other hand, rims require more time and effort to pack, and are hand-carried to the UPS Store for drop-off, so I have no qualms about collecting a few extra bucks for handling. I've been under the impression that the UPS price includes insurance for the declared value, but next time will need to verify this. I use commercially available 26x26x6 boxes that are actually too roomy. I could knock myself out making thinner boxes, but it wouldn't save any money.
Foreign shipments are a different story. USPS is expensive, but far cheaper than UPS or FedEx. The problem is shipping to countries like Australia where box girth plus length is limited to 79 inches. I haven't found a way to fit a pair of rims into a box of that size. It's odd that this rule should work out so precisely to the detriment of bike rims: 79 inches is just barely too small. It's odd, too, that the size restriction is lifted for their primo service, Global Express Guaranteed, (Global EXPENSIVE Guaranteed), but not for any other options in between.
I've seldom had to ship under this 79-inch rule, thankfully, because for me it means hand-making two boxes and sending one rim in each box via Priority Mail International. There is a significant cost savings in doing this, but it's a royal pain, and makes sense only because the rules are so cockeyed.
John Hurley
Austin, Texas, USA