Kids bedroom with adjoining play area. Lots of free floor space giving the children plenty of room to play on a soft area rug. Shelving creates a place to store books & toys, & hanging bubble chairs offer a cozy spot to "hang" out.
I plan on having lots of kids, at least so if space is limited, I just love the idea of having a loft bed built into the eaves of the house with two single beds below. It leaves a lot of floor space too, so no need for a toy-room.