I have a walking foot. It works great. With my machine I don't believe that I can use both at the same time. The walking foot will help evenly feed your fabrics, the ditch foot is nice for keeping you along the ditch but won't evenly feed from top and bottom.
Unless, of course, you have one of those machines that have a walking foot that can also have a ditch foot at the same time. Don't know what that one is but someone on here mentioned it sometime or other.