Promoters of a specific brand or formulation rarely publish the study information. There may be a difference but as I said, I don't believe that difference is detectable by the average person. The meaning of that comment is that nobody here will likely be able to say they saw a difference between brand/formulations. The experiences here would only be subjective.

If the claims made are important to you, then make your decision based on those claims. Is the claim based on a theoretical value or a benefit observable in users ? Is the improvement substantial or just a statistical value ?

Regarding a difference in quality, that can usually be addressed by looking at the label to see what concentrations of EPA/DHA are in that formation. If it does not show EPA/DHA amounts, I would not use it. Keep in mind that Vitamin E is important to help reduce oxidation of the fatty acid.

As goldenwillow said, there is a lot of research but I find it difficult to make sense of in a practical sense.