Hi I know this is an old post, but I am also debating between driftwood and rolling fog for my white subway tile. Did you choose, and if so what colour? Do you have an updated photo?

agree with previous posters..simple tile-blend the grout, as similar to the tile as possible..unless you deliberately want high contrast grout to accentuate it for some reason. then it becomes a decorative element on its own, and needs to be considered as such. more rustic tile that has different shape, like say star and cross mosaics, or lantern shape, etc-you want then a grout that's just a tad different in terms of shade, so it won't blend with the tile to the extent the effect of shape will be lost

It seems like your quartz is "quiet" so maybe you could have a more interesting backsplash. What is the flooring in the rest of the house?

Yep, as millwork man said get grout as close to the tile color as possible. Any contrasting color will highlight imperfections and make them more obvious.