this article makes BLE (bluetooth low energy) seem pretty attractive compared to ZigBee; BLE is said to have lower power requirements (it lists current draw for RF4CE but not for ZigBee, but it says that RF4CE is similar to ZigBee; RF4CE current draw is said to be too high for a CR2032 battery), better range, and better resistance to jamming; and BLE is said to be able to do mesh networking with the addition of an application)
M. Shetiya, N. Mane, P. Uplap, and P. Musale. International Journal on Recent and Innovation Trends in Computing and Communication, 3 (3):
1421--1424(March 2015)