I have to say that floor is driving the bus and never gloss tiles in a shower with kids. Is there a tile flange on the tub? Are you sure that tub was installed with perfect waterproofing for the shower walls ?

The tub shower unit in the picture is being replaced with a Kohler Underscore tub with tile above it on three walls.

neither.

certainly not the marble-look. not w/that flooring.

I'd do a 4x12 subway in soft white or a darker charcoal color.

maybe a darker taupe/tan color that works w/the floor

see these first two shower walls? something in this size tile and layout

see this busy floor and how the simple stacked white tile just blends into the wall?

Same premise w/this one if you wanted to use a darker tile to match that dark floor color

this dark charcoal isn't the right tone, but you get the idea.

You might be able to do something like these. Try the Portmore from Tilebar, or Cloe from Bedrosians.

Everything is so monotone. I'd bring in some wood shelves and some plants to punch it up a bit