A field experiment was done, using advanced technology:
So which company treats your packages with the most tender loving care? After crunching the data and averaging the number of spikes recorded by each carrier on each trip, we found that the USPS has the gentlest touch, with a per-trip average of 0.5 acceleration spikes over 6 g's. FedEx and UPS logged an average of three and two big drops per trip, respectively (see graph, next page).
Given those results, we were a little surprised to find that the USPS flipped over its Express Mail packages an awful lot, averaging 12.5 position changes per trip. Meanwhile, FedEx averaged seven position changes, and UPS had an average of four.
All three carriers did a good job at maintaining a stable temperature, but FedEx nabbed the top rating, with an average change of only 26.01 degrees, compared with 26.8 degrees for UPS and almost 32 degrees for the USPS. But the maximum temperatures our package experienced were within 2 degrees, and at no time did a temperature register above 80 degrees or below 47 degrees.
One disheartening result was that our package received more abuse when marked "Fragile" or "This Side Up." The carriers flipped the package more, and it registered above-average acceleration spikes during trips for which we requested careful treatment.
Here is much more, including a nice picture. At the very least, the packages seem to arrive on time.
For the pointer I thank www.bookforum.com.