I think the darker grout looks better. In your first picture the grout lines do not look inconsistent enough to matter. The darker grout does make the tile shapes pop. It will look beautiful.

I like the lighter one. With the darker grout it might look like chicken wire.

I personally like the lighter one... But I like subtle.

I am doing white subway, with marble hex flooring as well. I think the grout I am using is called warm grey.

IMO both grout colors look attractive. It just depends if emphasizing the tile shape is a priority to you or not.

Agree, do you want to empasize the size & shape? I did, so did a darker grout and am very happy with the look.

If you are concerned about differences in joint width the lighter one will be more forgiving.

Another vote for the lighter grout.

They both work with the tile, but give you a different look. I also prefer the subtle look.

Darker. The lighter one blends too much with the tile.

If you are using the same grout on white subways, I like the lighter grout. If you can do two grout colors (and I don't see why you can't), I would use dark on the floor and light on the walls.

What did you choose?