Code says the tub spout must be above the flood rim of the tub...so you can put it anywhere above that height. Get your other half to give you feedback on where it looks best. Also note, some of the valves have a minimum drop from the valve to the level of the tub spout...you do not want to make that shorter than the minimum or you may not be able to put the trim on, or spin the spout on, if you chose one that needs that (HJ and Terry like the Delta pull-down diverter tub spouts...I took their advice and put one in my mother's house, and she likes it, too). From a visual standpoint, it also should take into account the tile size and grout joint placement and whether you're going to have to drill a hole in the tile (and where - some tile don't like that at all!), or it will end up near a joint, and you can nibble out some from adjacent tiles to allow the pipe to pass through the wall. If you need to drill a hole in the tile, that's another tool you may not have. It can be done with a grinder from the back side, but that's more stressful and you may crack a few tiles while you learn the technique.