I use both because they are both for energy manipulation. I have heard those that say you can only use a sword or athame, while others claim you have to use a wand. Some people even have wooden athames (a step between a wand and athame).
I think it all depends on what you prefer, I find a wand less harsh, so I prefer to use this, but others will differ.
Honestly you don't need anything at all to cast a circle, so if hands are just as good as a wand or athame, I would say they were interchangeable.