It really depends on what you are doing. If you compare mA/MHz, the M3 will probably be lower than the AVR. If your micro is busy a lot, you maybe get lower pow

It really depends on what you are doing. If you compare mA/MHz, the M3 will probably be lower than the AVR. If your micro is busy a lot, you maybe get lower power consumption from the M3. If your micro is idle most of the time, the AVR lower power states will probably be more efficient than the M3.