What shades of grey should I choose?

To keep the room light, paint the light on top. If your furniture is dark, and will be against the wall, you may want to paint the light on the bottom.

My personal preference is light at the top and dark on the bottom :)

Thank you for your help

My preference is one color for all including the trim. Your walls will look much taller and the finish looks much more expensive. My trim is a bit on the wimpy side and one color really made it look nicer.

My first thought is that the light grey goes above and the darker below.