I decided to delve into the world of fats and oils for this nutrition info blog because there is a lot of confusion out there on this topic!
 
A tiny bit of history:
Humans, for tens of thousands of years, have depended on and used the fats from trees (olives, coconuts & palms), cows (butter, cream, tallow) and pigs (lard) to cook with.
Then, during the 1960's and 1970's scientists began to think that saturated fats were at the base of heart disease.  Enter the world of the polyunsaturates - vegetable oils:  soy, corn, safflower, and canola.  (to a lesser extent, sunflower and sesame).  It was thought that these oils would protect us from the dangers of high cholesterol and heart disease.  Wrong.
  
Without going into a very long explanation of how and why this didn't work to prevent heart disease, the latest research on fats is painting a very different picture.  We now know, beyond a shadow of a doubt, that those vegetable oils, especially when they are heated and used in deep frying, are very toxic, not just to the heart, but are also cancer-promoting.
 
Cutting to the chase....
 
THE GOOD:
Olive oil always has been and still is extremely healthful.  It is anti-inflammatory, immune enhancing and even has anti-pain effects that act much like ibuprofen (without the nasty side effects)
 
Coconut oil is solid room temperature and is therefore "saturated" but it is a healthful oil.  It is high in lauric acid which is anti-viral.  Although it is a fat, when consumed, it does not go into fat storage as most fats do; instead, because it is a medium-chain trigliceride, it is burned as a carbohydrate and therefore aids in weight loss.  Countries that consume large amounts of coconut oil have lower levels of cholesterol and better heart health.  It also supports healthy thyroid function.  It should be organic and non-hydrogenated.
 
Omega oils ... just the good ones, first
Omega 3s (fish & fish oil, Epa-Dha) and flaxseed oil; (grass fed animals have an appreciable amount of omegs3s as well)
Omega 6's (borage, evening primrose and black current seed)
Omega 9's (olive oil)
 
THE BAD:
The actual nut and seed sources of the omega6 oils are beneficial and necessary part of the human diet.  Seeds and nuts have a combination of 6s and 9s and are quite healthful when eaten as food, not pressed as oil:  sunflower seeds, pumpkin seeds, almonds, walnuts, sesame seeds, spirulina, leafy greens, soybeans, are good when eaten as foods.  But when you look at the process that a poor little seed or nut goes through to become an oil, you can understand why it becomes toxic.  They are put through an extraction process that boils, refines, bleaches, and de-odorizes, using chemicals and solvents.  Even when an oil says: "mechanically extracted", no solvents used, etc, it is far from good for you.  They can even be labeled "cold-pressed" after subjecting them to very high heat before the "cold-press" is applied to extract the oil.  It's this high heat that starts to turn the healthy cis configuration to a "trans" configuration.  Picture trying to wring oil out of a soybean.  Then picture how much easier it would be to wring oil of an olive.  You can see why the harder the object, the more rigorous the wringing/pressing process would have to be.  A tricky business, with many tricks on the labels of the vegetable seed/nut oils.  (the olive fruit is not only easier to press with less damaging machinery, it is also mainly an omega 9 oil which is much more stable and less likely to oxidize.)
 
Cheap fish oils.  If the fish oils have not been thoroughty cleaned and distilled through a molecular process and packaged with mixed tocopherols and stored in amber glass, it is likely to go rancid before you ingest it.  This would be worse than not taking it at all.  Eat wild caugh King Salmon as much as possible for this kind of oil and only take the highest quality supplemental fish oil.  When using fish oil, (Epa-Dha) you should also take a mixed tocopherol VitE capsule to insure it won't oxidize.
 
THE UGLY:
If you take the "bad" omega 6 plant oils listed above (corn, soy, canola, safflower, etc) and then fry potatoes, calamari, onion rings, etc, in them, then you really get the ugly!  The hydrogenation of these oils to give them a longer shelf life (all baked goods not made by you!) and used for deep-frying in restaurants, makes them pro-heart disease and pro-carcinogenic.
 
The largest source of the omega 6 oils for most people is found in salad dressings and mayonnaise.  One should always make their own salad dressing with the highest quality virgin pressed, small batch, small bottle, olive oil with lemon juice and/or high quality vinegar.  Restaruant meals are the biggest danger - they cook with vegetable oils and make salad dressings with them.  Just for an adventure, go down the salad dressing aisle at the market and read all the labels.  Even Paul Newman's "olive oil" dressing is mostly "vegetable oils".
It's best to avoid all packaged food (even if it states: no trans fats, don't believe it as they are allowed a certain milligram dose and still say "no trans fats") and all fast food.  
* interesting tidbit:  When McDonals's switched from beef tallow to partially hydrogenated vegetable oil for frying in 1990 (20 yrs ago), the percentage of fat that came from trans-fatty acids in McDonald's french-fries increased from 5% to 48%.  These trans-fats in french fries have been specifically linked to the rising rate of breast cancer in younger and younger women.
 
Bottom line:
We need all of the omegas - 3,6,9 for good health.  The ratio is the problem.  At the beginning of the 20th century, the ratio of 3s to 6s was 1:1 or, at most 1:2.  Today, it is closer to 20 times more omega 6 oils than omega 3s.  (cattle being raised on feed-lot corn & grains, consumption of less fish, store bought salad dressings, eating out, fast food, packaged baked snacks and treats of all kinds: crackers, cookies, cakes, chips etc)
 
For the good  Omega 3s, eat wild caught King Salmon once or twice a week and/or grind up some flax seeds every morning to put in/on whatever...
For the good Omega 6s, eat seeds and nuts every day.  One of the most healthful combinations are pepitas & walnuts.  Almonds also rank high.
For the Omega 9s, go for the organic extra virgin oilve oil in small amber glass bottles.  Trader Joe's sells a nice one made in Calif.
Other cooking oils should be coconut oil (for reasons mentioned above) and butter in small amounts.  Butter and coconut oil, 50-50 mixture works nicely in baking.  When sauteeing vegetables, coconut oil is the very best as it does not break down even at high temperatures.  Olive oil is good for saute, medium high temp.
 
 
Mary Anne