An electronic device such as a wristwatch may be provided with a wireless local area network (WLAN) transceiver, satellite receiver, and cellular transceiver. A first antenna may include a radiating slot between a conductive housing wall and a display module. A second antenna may include conductive structures that radiate through a rear face of the device. The WLAN transceiver and the satellite receiver may be coupled to the first antenna. A switch may be coupled between the cellular transceiver and the first and second antennas. Control circuitry may adjust the switch to route signals between the cellular transceiver and a selected one of the first and second antennas based on wireless performance metric data so that the antenna exhibiting superior wireless performance at cellular telephone frequencies is used for cellular telephone communications regardless of environmental conditions.