Flaxseeds are a whole food; flaxseed oil is not. Therefore, from my perspective, flaxseeds are superior when it comes to choosing a food that provides a host of different benefits. Let me further explain.
Flaxseeds and the oil made from them have gained great attention recently since they are a concentrated source of omega-3 fatty acids, specifically alpha-linolenic acid (ALA), the building block for all omega-3s.
It is true that flaxseed oil contains more ALA than flaxseeds (one tablespoon of flaxseeds contains nearly 2 grams while one tablespoon of flaxseed oil contains 7.25 grams). This, of course, makes sense since the omega-3s are present in the oil component of the seeds.
But flaxseeds are a whole food and therefore contain a host of other nutrients that are not included in its extracted oil. For example, they are also a rich source of dietary fiber; minerals such as manganese, copper, and magnesium; and vitamins such as folate and vitamin B6. In addition, they contain lignan phytonutrients, which have been found to have hormone-balancing and cardiovascular benefits. While some flaxseed oils have lignans added back to them, the resulting product is still different from its natural, whole-food form.
I'd encourage you to think of flaxseeds and flaxseed oil as unique and not as one being a substitute for the other. When it comes to a great food that can be incorporated into your diet that provides an array of different nutritional benefits, think flaxseeds. As for flaxseed oil, I view it more as a dietary supplement that can help people give their oemga-3 intake a large boost if they are unable to achieve their omega-3 goals through the foods that they eat. One warning about flaxseeds, though: the very small size of these seeds puts a premium on careful chewing. You cannot get all of those unique flaxseed benefits I described unless you can crush the seeds enough while chewing—and/or by grinding them first—to allow for other steps in digestion.