first I used grapeseed oil that I normally use for cooking, because I was so eager to get going and had nothing else at home. It worked quite well, produced all this amazing sinus drainage. Then for a month or so I used organic expeller pressed Safflower oil, ignorantly thinking it was the same as Sunflower oil. As far as I am concerned, it worked very well. Then I bought a bottle of organic cold pressed unrefined Sunflower oil which I have been using for the past month. It also works very well. I quite like the mildly nutty flavor of it, although the oregano oil competes with it.
I think all these oils work, it's more a matter of preference.