I would go with gray grout - white is difficult to maintain. I have white grout now and would never use it again. If you are iffy on the gray, just go with a lighter gray color...just dark enough so it doesn't look dingy. Good luck!

I have the Subway Ceramics Avalon / Minas with a medium gray grout. And a Shaw's white sink, if anyone is considering that, by the way. (My contractor could have ordered it directly, but at his request, I went through a tile store, and by the time everyone had put their sugar onto it, it was OBSCENELY expensive.) I'm not an installation expert, but at least with the Subway Ceramics, the installers use little plastic spacers between the tiles (I think some others have their own spacers?) when they put them up, they don't do it freehand, so how much grout you get is a function of 1) the limits set by the curvature of the tile and 2) what size spacers they use. So you might be willing to go a little darker with a smaller grout line, or with a handmade tile that refuses to go close together, you might want to stay light. The traditional color is close to concrete. But most modern people don't seem to like that, so do what pleases you!

I agree with the rest. If it were a checkerboard, that would be a different story. Black grout would be the thing-- either way-- black or white would look exactly the same, believe it or not. Black would be easier to keep up. but being that you have white tiles against white tiles, the black would be TOO much of a contrast. Go with a medium grey, something like Custom Delorean grey, or Mapei Pewter.

If those are the only 3 choices. The top one. But I would look for something slightly lighter than that one.