Neither 3 ohms nor 8 ohms is more powerful; the ohm is not a unit of power but of resistance to electrical current. However, an 8-ohm resistor has a greater ability to resist or reduce power.
Resistance to electrical current is often attained in electrical circuits with the use of a resistor. A resistor's ability to resist current is measured in ohms. Given a particular voltage, a higher amount of ohms means that there is a lower current flowing through the resistor. A decrease in current flow at a given voltage means a decrease in power. Therefore, a resistor with a higher ohm rating typically indicates a lower power output.