For a tile back splash I would use a moisture and mildew resistant drywall, such as a green board. Typically you are putting a tile back splash some where that might get "splashed" with water so it is always a good habit to be prepared. Of course tile will stick to any type of sheet rock but green board or hardiboard is always best is those situations. I use green boards in kitchen and around bathroom sinks where there might be a splash. I use hardiboard in showers where the moisture content is much higher. I hope this was helpful.