Healthiest oil to cook food in?

A lot of oils have great fats in them. However, some don't do all that well in cooking. For example, olive oil may break down in high heat.
M academia nut oil has a slightly higher breakdown temperature and tastes amazing and has much of the oleic acid that olive oil has. Be ready to shell out a few more bucks though.
The oil that has gotten lots of press is coconut oil. It has lauric acid in that is antimicrobial for an added benefit. The reasoning is that saturated fats don't break down that easy and need more heat. The breakdown effect can cause the making of trans fat.
However, my favorite is butter. Buy the organic pasture butter.. It has a high heat breakdown and has selenium, cla, vit k, micronutrients and soothes digestion. Weston A. Price thought of butter oil as one of the essences of health and longevity.

Obviously, depending upon your goals, use an appropriate amount of oil when cooking since it adds what are usually unnecessary calories to foods.

Having said that there are only two considerations: 1) smoking point - the temperature at which the oil degrades, which will have negative health and taste consequences and 2) the health and body-composition effects of the oil.

Most olive oil is OK to use up to over 450 degrees Fahrenheit. Even extra virgin is good to almost 400 degrees and canola oil, which is on balance probably just as healthy is good to over 450 degrees. These oils are high in monounsaturated fats and are probably the next most healthy fats after fish oils and flax oils. So go with extra virgin if you are going to cook at a low to moderate heat and go with normal olive or canola oil if you plan to crank up the temperature.

Hi
I personally prefer olive oil, there are obviously different types but shown below are the different ones and what they are good for and what their smoking point is. You should not let an oil exceed it's smoking point. One of the simplest ways to reduce the amount of oil you use is to put the oil into a spray, a couple of squirts is usually enough to coat a pan to prevent sticking, I always use the oil that way if I am dieting.

Olive oil (extra light) 242 °C (468 °F) Sautee, stir frying, frying, cooking, salad oils
Olive oil (extra virgin) 190 °C (374 °F) Cooking, salad oils
Olive oil (virgin) 215 °C (419 °F) Cooking, salad oils
Olive oil (refined) 225 °C (437 °F) Sautee, stir frying, cooking, salad oils