Many oils deteriorate at high temperatures and form free radicals which are bad for our health.
Some oils are perfect for frying at the high temperatures required for getting food exquisitely crisp. The very best oil I have found for this is high-oleic safflower oil. The Spectrum Naturals brand is made from oil extracted from high-oleic safflower seeds, which are cultivated expressly for this purpose. Be sure the oil is hot enough before you put the food in the pan. The telltale sign is that it will cause a bread crumb to sizzle dramatically upon contact.