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.
I would say yes, but as gopal.amlekar says: You will need drivers for the motors; the motors cannot be connected directly to the MCU pins.
-But most Cortex-M based microcontrollers from STMicroelectronics will have timers that allow you to create PWM signals, which can be used to control motors.
Like ackmicro says, try posting a list of things that your project requires, making the list as complete as you can.
-Then we'll all drop some suggestions, so you'll have something to choose from.
Chances are, that if you've already found a board that you like, it will probably be able to do most of what you need. The remaining part can probably be added easily as external devices.
-For instance, it's possible to buy a low-cost NOR Flash memory which you can use with SPI. This NOR Flash could be 512KByte for less than $1!