Such a nice question. I just asked that almost three weeks ago to somebody and mr google, and I found out that as if and as though is almost the same. I mean there's no difference that is why you can use any of them. But when I arrived here in US, a friend of mine told me that 'as if' is rarely to hear and some of them almost understand it as not acceptable. That's why I would advise you to prefer use "as though". :) Hope my answer could help! :)