I have 12V and 5V power available. Is it better to feed the 5V through the Vcc pin or either the 12V or 5V through the Vraw pin?
Use the 5V connected to the Vcc pin.
If you use the Vraw pin, the voltage goes through a voltage regulator. This voltage regulator will convert the higher voltage down to 5V by converting the extra volts to heat. So in case of using 12V you'd be throwing away around 60% of the power. Which is both wasteful, and will heat up the regulator quite a bit (depending on the load).