When you go to the store, it can be very confusing to see all those eggs. Free-range, cage-free, organic, vegetarian-fed. Which egg is best?
Chickens are omnivores. They will eat grain, seeds, plants, rats, bugs, and raw meat. In other words, chickens will eat almost anything they can find.
A cage-free chicken is kept out of the traditional "battery cages" commonly used on factory farms. Battery cages are tiny cages that aren't even big enough for the chicken to turn around. Even if they are not kept in a battery cage, these chickens might be living in a crowded barn where they never see daylight. A cage-free egg does not mean it's a good egg.
A vegetarian-fed chicken is only fed a vegetarian diet. It used to be quite common for farmers to throw back the unusable parts of butchered chickens outside for whoever was around to eat. Thus, chickens were eating chickens. Due to public outcry after mad cow disease, where cows were eating cow parts, most farmers stopped feeding meat to their animals. Still, vegetarian-fed eggs are not the best options because of the feed. The grain is usually cheap, which means that it's commonly genetically modified and has been sprayed with pesticides.
An organic egg is from a chicken that's been fed an organic diet. These chickens are not administered hormones or antibiotics to increase egg production. This is a better option, but it is still unnatural for a chicken to only eat grain.
A free-range chicken is allowed access to the outside. Chickens are not meant to be cooped up, like they are on factory farms. Free-range chickens will scratch to find their food. True free-range chickens make the best eggs for 3 reasons: they get sunlight which gives them vitamin D, they are allowed to run around and get exercise like any animal should in nature, and because they are eating natural foods.
You can usually find free-range eggs at any grocery store or superstore. However, it is hard to know how that producer defines free-range. The United States Department of Agriculture does not have any specific rules on how much time or space the chicken must be allowed outsde. Egg producers might simply leave the door to the barn open, or let the chickens go outside on a concrete slab. It's hard to forage on concrete. For this reason, it is best to buy eggs from the farmers' market. Then you will be able to talk to the farmers about how they raise their chickens. Small farmers generally treat their animals well and allow them to live as nature intended.