If you have 3 bars and above on LTE it might actually be better to leave LTE on since the power management takes care of the rest. However if you have less than 3 bars then leave it off if you're not near a charger, the device will strain itself trying to get a good signal.
I guess it might be hard to quantify, but I listen to an Internet radio station at work. So one morning, I listened to an hour on LTE, then an hour on 3G. Both used 30% per hour, based on starting at 100%. This was in a location with 1 or 2 bars, so lousy signal. Using wifi was negligible, when I tried at home.