Extra virgin olive oil has strong antioxidant properties because of the numerous phytonutrients in the oil. There are even some important antioxidants that can only be found in extra virgin olive oil. The amount of phytonutrients (which includes polyphenols) varies in extra virgin olive oil due to certain olives naturally containing more than others.
More importantly, however, is the process of producing extra virgin olive oil. Keeping a close eye on the process, from picking to pressing, is vital. The best growers nurture their olives, producing a great tasting olive oil time and again that is also high in phytonutrients. The artisan growers excel in this area.
Compare EVOO to the lowest-classified olive oil and you discover a noticeable difference. Olive oil is refined and heated treated, destroying the micronutrients along with the taste. Olive oil, while missing all the valuable micronutrients, is still useful (as it is a monounsaturated fat), but the quality and flavor cannot compare to that of the extra virgin classification.