Minami Nutrition, who use an extraction process without any heat, to fully preserve the Omega-3 from fish oils, recommends a ratio of 756 mg EPA to 228 mg DHA for *healthy* people:
But personally, I can't tolerate DHA, only EPA.
Personally, I found Minami's pure 500mg EPA product superior to Vascepa's synthetic prescription 1000mg EPA, for cognitive benefits. (not sure why they're so different)
There do seem to be significant problems with the quality of most fish oil supplements, and one possible reason is that these oils may degrade rapidly with exposure to oxygen or heat.
I don’t like to endorse specific brands, but I have been impressed with the quality of Minami brand omega-3 products. They don’t use any heat in the processing of their products, which may be one of the reasons for the high quality. In the U.S., these products are distributed by a company called Garden of Life. They are expensive, though.