So, the main three Omega 3 fatty acids are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). I’ve read a bit about them and I have noticed that their positive effects overlap quite a bit. Maybe some off you could accentuate what positive effects each one of them have?
Oil from fish, flaxseed, algae oil, and walnuts are healthy sources of omega 3. When we study real people in the real world, these are commonly what people consume in trials. Overall, the O3 in these foods tend to improve outcomes (such as cognitive outcomes which are commonly associated with O3).
I’ll leave the nuance of different types of O3 to other posters, but for me it’s not worth the time. I want data/research I can apply to my own life, and that means knowing what actual edible FOODS I should consume or avoid. In that context, the above suggestions are generally the source of O3 recommended by guidelines.