It really depends on the look that you are trying to achieve. Using the same tile on the floor and the shower will keep the space more open/ contemporary in nature, though less interesting. Tiling to the ceiling creates more of a sense of luxury, but stopping the tile mid-way (perhaps 1/3 of the way up the window) gives more of a sense of appropriate scale and is more welcoming. Mixing tile opens up so many more possibilities and options. Try playing with size differences if not color and texture. Even adding a moulding- pencil or ogee- to a few key areas (backsplash, accent banding, top of tub surround, framing shower nicho) in a contrast stone or material (glass?) adds a bit of interest while still keeping things simple.