Which part of the vertebra bears the most weight when someone is in a standing position?

The vertebral body is the part of the vertebrae that bears most of the weight when standing. That is why there is a fibrocartilage disc between the bodies of the vertebrae, to absorb shock and disperse the pressure. The facets do support some weight, particularly when the spine is moved into extension, however the facets are primarily to limit and direct the motion at each vertebral level.