Purely preference as to color.

Now when you ask us wide open questions like this, You invite the silliest of answers, and I have to go now because i am biting my hand not to ask about things like dancing piglets and.......oh bye!

I think it is all personal preference - one thing to ask your tiler is also the cost difference in laying different types of tiles. We see our clients using a lot more of the dark, larger tiles. There can be significant cost differences in tile setting costs depending on the tiles, so it's also good to coordinate your choice along with your budget and the estimate from your contractor.