First designer has it right about the direction of natural light . The white you choose for the south light won't show the same in the east light. She is choosing a white the best undertone for each room.

The second designer is suggesting one color for the house. But, natural light in each room will change that color, as well.

If you want white stick with #1.

If you want one color, look at B.M. Collingwood. It is a pretty flexible. It is in the gray family, but different natural light can turn it into a greige. I just used it in a client's open floor plan. Very nice.

I would challenge the logic of selecting different whites for each room.   

When selecting your white, it should be a white that works well with your flooring, cabinets and counter tops.  

The color and quality of light changes from room to room, but that impacts the colors of everything in the room.  Is she changing the flooring in each room?  It will look warmer in some rooms and cooler in others.  

If you choose a white that works with the floor and the light is very warm, both the flooring and the walls will appear warmer on that room, but the will look good together.

If the lighting is very cool both the flooring and the walls will appear cooler, but will work well with each other.

IMO the same color everywhere since every space has items that will affect color. A bigger issue for me is the lighting and I like all LED 4000K to keep colors true all the time . Some of my clients like 3500K that IMO is a low as you go anything under that will makes every white look yellow. Use the same color everywhere and make your life simple, I promise you that will look ggo in every room and cost you a lot less money for the paint job. Are you doing white because its 'IN" or because you love white for walls?

Thanks all. I do want white walls. Makes things clean and simple in my view (although not as simple if we go with different shades of white paint colours). I do take your point Jennifer that lighting would affect how the floors look as well, which of course we are not changing from room to room.

Just pick one white if you are mostly happy with how it will look throughout your house.

I've gone as far as painting one wall in a room a slightly lighter color due to lighting. With the lighter color on that one wall the room looked like all the walls were painted the same color. It does complicate things more compared to having to remember just one color for touch ups later on.

I would just make life simple and pick one. Paint colors change by amount of light, time of day, season, night time lighting. I've never thought rooms looked different colors when painted the same color white, and I doubt you could pick whites perfectly so that they would transition the same in all the different lighting situations. Although I also wouldn't paint all of my walls the same color either...

The fact is, a single color in a single ROOM will look different depending on the time of day and which wall you are looking at. I would suggest painting a large sample on a poster board and place/observe it on different walls during different times of the day. The only reason why I would advise different shades of white is IF the hard finishes (flooring, cabinetry, countertops) have different undertones and the white paint undertone would clash--again, you will be better equipped to see if you look at the proposed paint color on a large sample board next to the hard finishes in the room.