The best fish oils available are the liquid forms. Contrary to many people's expectations, the best liquid fish oils have no fishy odor or taste.
I use a lot of liquid fish oils because of the higher doses we use in the Track Your Plaque program, as well as our strategy of high-dose fish oil to reduce lipoprotein(a). Women, in particular, don't like taking the oodles of capsules required to achieve the higher doses we need. So the ladies really like the liquid forms.
The best liquid fish oils are non-fishy, highly-concentrated, and come in the better absorbed triglyceride form. Many capsules, including prescription Lovaza, are the less well-absorbed ethyl ester form. Several studies, such as this one, have now demonstrated that the naturally-occurring triglyceride form yields higher blood (RBC) levels of omega-3 fatty acids, likely due to more efficient digestion via pancreatic lipase.
While there are many good forms of fish oil and only a few bad, these are the best of the best:
Pharmax
The Pharmax Finest Pure Fish Oil with Essential Oil of Orange contains 1800 mg EPA + DHA per teaspoon. This is the preparation I've been taking.
Nordic Naturals
The Nordic Naturals lemon-flavored ProOmega Liquid contains 2752 mg EPA + DHA per teaspoon, the most concentrated of any fish oil I've seen.
(This list is not exclusive. These are just two brands I've used extensively with good results.)
These highly-concentrated, triglyceride forms are more expensive, due to their concentrated nature. 1 teaspoon Pharmax fish oil, for example, provides an equivalent quantity of omega-3 fatty acids as 6 standard fish oil capsules on a milligram for milligram basis, but more like 8 to 9 capsules when absorption efficiency is factored in. The triglyceride form is also more laborious to manufacture. On our Track Your Plaque Marketplace, our Pharmax 500 ml runs $58.95 list. (500 ml provides 100 teaspoons or 600-capsule equivalent.)
Note that, minus the protection of the capsule, liquid fish oils will oxidize if not refrigerated. So be sure to keep your liquid fish oil in the fridge.