UPS is a larger company globally than FedEx, and has a slightly higher percentage of packages delivered on time. While FedEx has a larger fleet of airplanes, UPS's ground fleet of trucks is almost five times the size of FedEx's.
Large shippers tend to choose UPS for ground delivery and FedEx for deliveries that require air service. According to Diffen, Apple uses FedEx more often, while Amazon uses UPS more. FedEx is also chosen more often for international deliveries, despite UPS's larger global presence. Fast Company points out that FedEx's air service offers the greatest reliability and that FedEx's ground service offers the best price. In general, however, the prices charged by the two companies for the same delivery route tend to be fairly close.