Whether chia seeds or flax seeds are better depends on the specific nutrition values being sought, but chia seeds are more convenient and offer a few more nutritional advantages than flax seeds. However, both seed types are nutritional powerhouses with unique benefits.
Since chia seeds do not need to be ground like flax seeds to obtain full nutritional benefits, they are more attractive from a convenience standpoint. Additionally, chia seeds are lower in calories, higher in calcium, phosphorus, and cholesterol-reducing fiber. Chia seeds are also one of the few plant sources of a complete protein. Flax seeds are richer in lignans, which have been linked to reducing risk of cancer, and are higher in copper and omega-3 fatty acids. Unless an individual is targeting one of the specific advantages of flax seeds, chia seeds have more advantages overall.