The answer to this question should always be after. The reason you want to tile after is because you will not know the starting line for your tile until after the countertop is installed. It is a lot easier and less expensive to make an adjustment to your tile backsplash than it is to change your countertop. Your countertop will be fabricated offsite where as your tile is done at your home. If an adjustment needs to be made to the countertop there is a good chance it may need to have to go back to the shop. A good tile company can adapt to any change in the layout of your backsplash.