Eggs are an excellent source of protein as well as certain vitamins and minerals otherwise found mainly in meats, making them a near perfect replacement for vegetarians. The only disadvantage is that although being a good source of iron, the type of iron in eggs called non-haem iron and is not as well absorbed as that in meats.
There are a couple of popular misunderstandings about eggs however, the first being that because their yolks are rich in cholesterol, many people avoid them thinking that they will raise blood cholesterol levels. As it turns out, our blood cholesterol becomes elevated when our liver produces extra amounts in response to the consumption of saturated fats, found largely in fatty meats and creamy dairy foods. Most peoples cholesterol levels will not rise much when they eat cholesterol, and can consequently enjoy meals containing eggs and shellfish several times per week without much effect. A small portion of people will respond to cholesterol in food however, and because you will not know whether you are one of those people or not, the National Heart Foundation has taken a conservative recommendation by advising people with elevated cholesterol not to eat eggs more than twice per week.
The other common myth about eggs is that when consumed raw, they can enhance athletic performance – a fad popularized in the 1970's by the movie ‘Rocky'. There is certainly no nutritional benefit to drinking raw eggs - in fact it can deplete levels of an essential vitamin called biotin as egg whites (albumin) contains a protein called avidin which binds with biotin, making it unavailable for absorption (avaidin is destroyed simply buy cooking it). The other major hazard associated with uncooked eggs is that it can potentially result in salmonella poisoning (salmonella will also be killed simply by cooking it).
Free Range vs Battery
Many people (including myself) consider free range hen farming to be more humane than battery farming, though even some free range farms have been criticized for animal cruelty (concerned Australian shoppers should chose brands with the RSPCA logo in it). Consumer have the option to choose to pay more for eggs which have come from free range hens as apposed to battery hens due to ethical considerations. There is no evidence however that the nutritional quality of free range eggs are significantly different to battery varieties. Whilst some people believe that they can distinguish the difference in taste between the two, it is unlikely that they can, as blinded studies show that many people detect nonexistent differences when they believe that a product will be different, even if it isn't.
The only major influence on taste and nutritional quality (as well as colour) is the diet of the hen. For example, hens fed more vegetable matter will produce darker coloured eggs rich in carotenoids, whilst those fed a diet high in Omega 3 fatty acids (from flax) will produce eggs with higher levels of the Omega 3 alpha linolenic acid (ALA). Whilst these may give the eggs modest nutritional benefits, eggs are not a significant contributor of carotenoids or Omega 3 fats anyway, with fruits and vegetables being a far better contributor of the former, and fish being a much better source (both in quantity and quality) of the latter.
The bottom line is that when eaten in moderation, eggs can make a healthy addition to a balanced diet - just be sure to cook them first.