What ever turns your crank, Thats what I always say, BUT normally the wall tiles are smaller than the floor tile, One other thing is the bigger the tile the smaller the job, I just did a full bathroom, and it was a major project, I used 12 X 12 on the floor and 6 1/2 on the walls 4ft up on walls and about 2 tiles higher than the shower head in shower area, it looks real nice, you may want to tape some tiles up just to make sure you like how the big tiles look??? It may look kind of od??? Good luck with your project