Bedroom with loft. What a great use of space for a room with a vaulted ceiling. A walk in closet could be under that loft and you haven't lost any space. ** Could be a good office space, with the bed up in the loft.
My older two boys share a room and sleep in bunk beds. Since we moved them to bunk beds it's been great as it has opened up a ton of space in their room for quiet time away from the chaos of the rest of the house. I love bunk beds.