You should have 2 main oils in your home for cooking: Olive Oil & Organic Canola Oil.
Olive Oil should be the oil used most often and in low-heat cooking; the best to use is extra-virgin olive oil (EVOO). EVOO is derived from the first pressing of the olives and has the most delicate flavor and most antioxidant benefits. It is one of the most healthy foods, protecting against degenerative diseases and heart disease. The mediterranean diet is very high in olive oil (it is their primary fat intake), and interestingly enough, these people are the most healthy and live the longest. But, do remember, it is a fat and should not be consumed in great quantities.
Organic Canola Oil should be used when cooking at high heat and, of course, when baking. Even thinking about brownies with olive oil makes me cringe! Canola Oil does not have all the health benefits of olive oil
Both of those oils are monounsaturated fats and should make up no more than 20% of your total fat intake.
Examples of polyunsaturated fats are liquid vegetable oils and should make up no more than 10% of your total fat intake.
Saturated fats include animal foods and coconut and palm oils and should make up no more than 7% of your total fat intake.
And, trans fats are things such as shortening, margarine, crackers, and cookies and should make up not more than 3% of your total fat intake.
Information taken from Dr. Low Dog.