Agreed that 3g will use less battery. Just my thought but... I think the trade off of using LTE consistently and the battery loss/usage from using it is worth it and the battery loss is typically pretty minimal.
The biggest battery drain that I notice while on LTE is that when I'm in a poor reception area and the signal is weak and is constantly switching from say, LTE, HSPA+, HSPA or 3g. etc. That's when I notice the most battery drain.
Personally I prefer LTE as my preferred data connection and the better data connections/speeds for me are well worth it.
There are other areas of the device that can be tweaked and adjusted to save battery instead of sacrificing your Data connection speeds.