Depending on the wifi networks around you, 15 and 20 are usually the best Zigbee channels to use. 25 is above wifi channel 11, but is lower power due to regulation. 26 is rather often not even supported on many devices.
EDIT: I too have over 60 Xiaomi Zigbee devices and they are all very snappy. For a good and recent thread about Zigbee channel change:
