Depending on your house style and how it would work with the 3 different measurements, you could look at doing a herringbone style pattern for example:

It will look wonderful love the simple tiles, as before run the tiles across on the floor/shower and back wall and running across the side walls will match to the rear wall tiles ie: run the same way. your tiler should know exactly what to do, I have a couple of photos for you to see how the tiles work starting from the floor, look forward to more photos cheers

If the hexagon tiles are to be the feature then the wall tiles should not draw attention to themselves. I would go with stacked horizontal as this will make the small room seem wider and it will be a simple grout pattern that won't try and compete with the hexagon mosaic. For small bathrooms understated and simple always looks cleaner. Best of luck, Dr Retro of Dr Retro House Calls

This may sound horrible but I keep thinking black tiles definitely where the range hood is going . ...could it be The hero of the kitchen area ? The rest of the tiling in white but not to the ceiling ( too commercial or bathroomish for my liking ) ..I would consider white floating shelves on the narrow walls on either end of your windows to add practicality to the modern look . As for Tiling...the area you have is generally is not a large space for tiling unless you go to the ceiling so I would keep the tiling low no matter which design you choose stacked or other. However, I would tile the range hood area up to the window line (in white to complete the white tile look or black to make the big bold black range hood stand out and take centre stage .) I also love Herringbone tiles for modern kitchens /bathrooms. But not knowing how busy your bench is plain stack may be the way to go . Good luck ENJOY your kitchen !