If there are any defects on the walls, flat paint will not highlight them like some other sheens. I've always preferred the look of the flat paint in every room except the bathroom. I would consider a low sheen or semi-gloss. The last time I painted my bathroom, I used BM Pearl Finish (which I've been very pleased with).

Thanks, that's sort of what I was thinking as well. On the textured walls, a light sheen was rather nice, but I'm less sure on the completely flat walls...

Flat paint will offer no washability as you have seen. Not just that, but if you bump in the walls, that will show as a dull spot and before long with many people bumping into the walls, there will be many dull spots and this can eventually look bad, especially on smooth drywall and if there is any natural light cast down that wall. There are low sheen washable paints now....some are not that good, but Aura Matte is very good. A washable paint, even one with an almost flat sheen, will be more resistant when people bump into the wall so that those dull spots will not show up as easily. Eggshells are good for bathrooms or matte would be okay in there too if you are not the type that likes a shine on the walls.