How do I select a microcontroller with low power consumption?
-for MSP430 series we can compare using \$\mu\$A/MHz at active state.
Similarly how to compare this with other MCU's like PIC and STM series i.e. other MCU's provide \$\mu\$A/MHz @ diff speed and have DMIPS for performance and MSP430 series doesn't provide any DMIPS parameter.
If \$\mu\$A/MHz==\$\mu\$A/MHz for ARM and MSP430 is it good to select ARM, as ARM is 32 bit where as MSP is 16 bit MCU?
First, you have to decide power consumption in which state matters for you.
There are several cases:
sleep-mode, possibly with some peripherals left running (an RTC, a timer, a PWM output, etc.)
very low-speed clock mode used instead of sleep-mode, with some peripherals left running
normal (high) clock mode, with the desired peripherals
Checking the exact power consumption (including the needed peripherals, as they can make a big difference) from the data sheet, reading and evaluating both typical and maximum figures is the way to go. Using generic (\$\mu\$A/MHz) figures will probably get you only a general answer.
