I've used both. The MSP430 has a few advantages over the AVR family when it comes to low power.
1) There are specific low power designs. They use lower voltages, which allows you to squeeze more energy out of each battery, and they use non-volatile RAM.
2) There are a lot of MSP430 variants, and they have integrated all sorts of features that would have to be external on an AVR series microcontroller. E.g., a real time clock, or an LCD driver.
3) The MSP430 series has variants with almost any quantity of digital or analog IO you could wish for. This means you can directly connect the MSP430 to things that you would need a breakout board for on an AVR.
So even if the AVR series and the MSP series are on relatively equal ground when it comes to power per clock (which they aren't), the MSP430 is a much better chip for low power draw.
1) There are specific low power designs. They use lower voltages, which allows you to squeeze more energy out of each battery, and they use non-volatile RAM.
2) There are a lot of MSP430 variants, and they have integrated all sorts of features that would have to be external on an AVR series microcontroller. E.g., a real time clock, or an LCD driver.
3) The MSP430 series has variants with almost any quantity of digital or analog IO you could wish for. This means you can directly connect the MSP430 to things that you would need a breakout board for on an AVR.
So even if the AVR series and the MSP series are on relatively equal ground when it comes to power per clock (which they aren't), the MSP430 is a much better chip for low power draw.