I personally think that sitting when meditating will increase your focus while laying will make you fall asleep. That's why I do both for different types of meditation.
It doesn't matter if u r sitting or laying down it depends on u what u are comfortable with , do anything u like but make sure that u r relaxing your body
I recommend lying down in the evening after a long day, it is much more comfortable than to sit. But if u plan to meditate in the morning i would say to sit.