I use safflower oil. I don't care for sunflower oil, I think it has a bitter aftertaste. I don't know why NT doesn't suggest safflower as an alternative along with sunflower, the mono/poly ratio is the same (you can get both oils in a high monounsaturated, high-oleic version). You can also use a pinch of dry mustard powder instead of dijon. The way I like it best is using a whole egg, mustard powder, Real Salt, apple cider or rice vinegar and safflower oil. BTW, the mustard isn't just there for flavor, it helps emulsify.