How do I decide which ARM board to go for if I am aiming to use it as a micro-controller to run sensors, actuators, motors, and solar panels? And I wish to power up the board via Li-ion battery pack.
If you have experience with Arduino in the past, you could always consider using an Arduino Due, which has a Cortex-M3 based processor and can be programmed from the Arduino IDE. It supports 3.3 V shields so if you have any from other projects, you could reuse them. Just an idea!
That is a good point. I forgot to mention that the LPC1549 boards from Embedded Artists also have arduino compatible pin headers.