There are no right or wrong answers to this question; it’s a matter of taste. However, this is a very important decision and one that should not be taken lightly. Warm white provides a cosier, warmer appearance, like a candle. On a scale, a candle would be 2200 kelvin and the sky would be 6500 kelvin.
Traditional halogen an incandescent light bulbs are more of an extra warm white 2700K colour temperature. Going for 2700K or 3000K is often the safe option and I believe that 3000K has become the new norm. In a few more years people will become more used to LEDs and will think halogen was too warm. Cool white is much clearer in appearance and can seem harsh, it can make a room feel too clinical like a dentist surgery.
If you want to for a more modern appearance then used correctly cool white 4000K can bring out the room’s alter ego as colour temperatures accent the colours of the room. Although their is usually just a few lumens difference in light output, cool white can make a room appear much brighter.
Further down the colour temperature scale is daylight 5600 to 6500 kelvin which is bordering on the bluer end of the spectrum. This is an ever harsher white colour but used correctly can provide an almost post modern appearance. Each colour temperature can be used effectively in the right room setting. The pictures in the video below compare the main three being used in the same room: