So, after a little googling around.
Cellphones typically transmit on 3/4 G at between 0.3 and 3 W - subject to tower location & interference. The out put power is managed by the cell tower.
Mobile phone wifi is typically 15mW.
If we assume min output for 3/4 G at 300 mW (0.3 W) this is, at best, 20 times greater than wifi at 15 mW.
On that basis I would expect wifi to be the more energy efficient medium.
However protocol efficiency also plays a part. The simplest crude measure of this is probably to time how long each channel takes to recieve the same block of data and scale the power usage accordingly. Note that subject to your data plan upload / download speeds will usually differ & so there may be different results for each direction.