I run a business that ships numerous packages weekly, all of which require Next Day Air shipping. Given that I ship perishables, it is crucial for my packages to arrive in a timely fashion.
UPS offers about a 40% chance of that happening, based on about 2 years of service with them. I have since moved on to DHL and Fedex, both of which have provided me with aboiut a minimum of 80% success rate. The savings were minimal with UPS, and were by far outweighed by the devastating losses incurred.
For those seeking reliable Overnight shipping, Fedex and DHL are much better bets.