I've been taking fish pills about 2/day for several years. It seems to make me feel a little better than not taking them. I take this brand called Natural Factors. They're not the most inexpensive but they are a lot less expensive and seem just as good as Nordic Naturals which are really expensive.
I haven't used Krill oil, but as long as the oil contains adequate EPA and DHA oils and no fillers and is molecularly distilled, pharmaceutical grade and pure, I don;t think the source matters.
Our food and diet is low in Omega 3 essential fats, and fish can be contaminated with mercury and other stuff, so I think most people could benefit from some supplement.