Running bond is more forgiving, since you don't have to worry if the vertical joints line up exactly perfect. Are you only doing two rows, though? If so, I think stacked would look better, and it shouldn't be hard to keep the joints perfect. The row of mosaics in between the top row and the rest gives you some leeway, too.

Thanks for weighing in, catbuilder. My DH decided he prefers the grid layout saying it will go better with the beadboard wainscoting, so we are going with the grid.

I can't wait to get the tile up yet I'm a nervous wreck that I will screw it up!