It is an absurd statement to say that most fish oil is rancid....As absurd is to recommend an oil with omega 3, 6 and 9. That is ridiculous...
The main reason to take omega 3 is to balance for the enormous quantities of omega 6 our modern foods have, and now you are going to add more omega 6 with your supplement. Non sense.
You should only take supplements with omega 3, not omega 6 or 9. Those last will make you fatter and less healthy.
You have good, medium and low quality omega 3 like in any other product. The best quality omega 3 is the molecularly distilled fish oil, has no contaminants.