The simple answer is always full speed, which consumes more electricity.
This is the long answer.
Ceiling fans are not the only ones that consume more power. If you have a 100watt fan, 100watts of power will be consumed if it is running at full speed. The fan can be connected to a regulator so it runs at half speed and consumes 50 watts of power.
You might argue that regulator power consumption should also be considered. The regulator’s job is to increase fan resistance.
You can solve the problem by using the formulas below.
P=V*I
V=I*R
Where is it?
P=power, V=voltage, I=current, R=Resistance
My handwriting is fine.
Below, I used 100watt fan with 200 ohm resistor regulator to achieve 72watts power consumption
You can achieve 57watts power by applying 400 ohms resistance. This will slow down fan rotation and reduce power consumption.