Now you know.
LTE, 3G or Wifi?
According to
this article by Huang et al., and based on their usage scenario, LTE is the least energy efficient protocol, then comes 3G while Wifi offers the best energy efficiency. Under the test scenario, LTE consumed 5 to 12 times more than Wifi and 3G 5 to 8 times more.
Also, uplink on cellular network consumes much more energy because your signal has to reach a distant tower. There is a comparison of uplink/downlink power consumption for the 3 technologies in this article (figure 9). The conclusion to this is that you should refrain from uploading data to the "cloud" while on 3G/LTE connectivity.
I read somewhere that turning Wifi is bad because with cellular already on, that means you now have two power hungry processes. This is a wrong interpretation of how communications work. Power consumption rises up only during transmission, while idling is designed to be energy efficient (figure 3). Therefore, using Wifi to transmit data should save you energy even though cellular is on at the same time.
Remember that your local network coverage can significantly alter these results. Poor Wifi might result in increased power consumption and cellular data might then become more interesting.