Firstly - use a fresh oil! Do not use anything that's been opened for a long time and when you store oil, it should be in a cool dark place. Light and heat accelerate oxidation reactions that can make the flavor turn rancid. My oil of choice for baking is sunflower oil for its clean and neutral taste, but any other oil such as canola or safflower will do. You can even use olive oil, but keep in mind that it will add the taste of olive oil to the cake.