I agree with
@HopperFan on the details. The only thing I would add is that the preferred room bookable category are all AB rooms, which are the closest to the lobby and food court. We have stayed in these rooms and particularly liked that the buildings are smaller and somewhat spread out with beautiful landscaped areas between them. The mansion buildings are larger and taller so the rooms are more densely packed, but inside the room the size and floorplan is the same. As far as proximity to the lobby and food court, AB rooms can be the best or the worst, depending on how far out they are. Most of the Mansion rooms have a walk that is somewhere in between.
I completely agree that you should go with the theme you prefer most, given availability and your choice of bookable categories.
Royal rooms are all in the mansions and tend to be the most expensive, but you get the fancy touches like lights and decorations.