I would go with the light one. That tile looks like the grey version of the one we did (the blue). A slightly lighter grout helps accent all the beautiful irregularities in the tile.

Using a matching grout will make it appear as one solid sheet unless you are right up close. I prefer some definition and would go with the lighter colour, but it really is a matter of personal preference. I think I read something about the grouts with glitter having some sort of problem, but can't remember for sure - you might want to google it.

I like the lighter one but I think it would look fine with any.