Since flax seed is very stable when whole, but important fatty acids are heat sensitive once ground, I always buy whole flax seed (typically in bulk), at the supermarket. While I store it in the freezer, I grind enough for a week (using a dedicated, $8 coffee grinder) to keep in a glass jar in the refrigerator, for easy access. Health wise, there doesn’t seem to be a difference between brown or golden flax, but in baking, if you are concerned about keeping your recipe light in color, use golden flax.