So, you have heard about all the health benefits of going low carb, and whole, natural foods but you are a little confused with all of the different choices of eating lifestyles out there? Let me try to sort them out for you; kind of a TL;DR version of the most popular whole foods eating options, if you will.

Overview: The Paleo Diet, originated by Loren Cordain, is based on the notion that humans have not evolved to eat foods that were not eaten during the days of our ancient hunter-gatherer ancestors, prior to agriculture. Followers of The Paleo Diet shun grains, legumes, processed foods, artificial sweeteners, vegetable oils and dairy products. Animal proteins consumed should be grass fed or free range. This is not considered a low carb diet, per se, as it allows certain foods like fruits, some tubers and root vegetables and honey as eating options, although it can be adapted to be low carb. This way of eating tends to be the lowest in fat of all the whole foods based diets.

Who Is It Best For: The purist. Anyone concerned with the humane treatment of animals. Former veg*ans. Those with autoimmune diseases and dairy sensitivities.

Who Should Use Caution: Anyone overweight or diabetic should avoid most fruits, starchy vegetables and honey as these foods can spike blood glucose levels. Also, those with GERD may find these allowed foods to cause heartburn of an extreme nature.

Pros: Whole, nutritious foods.

Cons: Grass fed and free range proteins are expensive.

More Information: 
The Paleo Diet
Wikipedia: Paleolithic Diet
Robb Wolf

Overview: Very similar to Paleo, The Primal Blueprint was laid out by Mark Sisson, and is also a whole foods based way of eating, though it allows more flexibility with its 80/20 Principle ("...if you're eating fully Primal 80% of the time, the other 20% offers room for well-intentioned but practical choices when we can't be Primal or choose not to be for a variety of personal reasons." link). Mark's nutritional approach gives different options for those wanting to lose excess body fat to those who are lean and very active in regard to carbohydrate intake. The Primal way of eating doesn't necessarily get hung up on the whole grass-fed, free range thing, or the total elimination of dairy products, and leaves it up to the individual to decide their animal protein sources and butter consumption. It is a decidedly higher fat way of eating than Paleo, but does stress healthy fat consumption (e.g., shunning rancid vegetable oils and instead using natural animal fats, olive oil, coconut oil, etc.). A very human friendly, ability friendly way of living.

Who Is It Best For: Those transitioning into whole foods eating from a Standard American Diet (or any other typical government recommended diet, Sweden excluded), and overweight and diabetic persons as long as a lower carbohydrate option is implemented.

Who Should Use Caution: Anyone who has carb cravings after eating fruits should steer clear of eating them even though some are allowed in this way of eating.

Pros: Whole, nutritious foods and flexibility.

Cons: The 80/20 Principle is easily abused and can lead to major carb-creep if not kept strictly in check.

More Information:
Mark's Daily Apple
The Primal Blueprint
Mark's Daily Apple Forum

Overview: The Ketogenic diet was first discovered to be an effective regimen for the control of epilepsy in children in the 1920s. These days it has been found to be an effective way of life to lose weight, maintain weight and improve health markers. The way of eating is also referred to as "Low Carb, High Fat," or "LCHF."  It is a high fat, moderate to low protein, very low carbohydrate diet, with the recommended ratios of macronutrients being 70% to 75% fat, 20% to 25% protein, and 5% to 10% carbohydrates. Ketosis and becoming Keto-adapted (where the body burns fat as its preferred fuel as opposed to glucose) are the goals and outcome for those who keep their percentages within the guidelines. Well sourced animal proteins are suggested, as well as natural low carb sweeteners instead of artificial ones, and good animal fats and other fats like coconut oil instead of vegetable oils, although not everyone follows the same school of thought on these matters when adhering to a Ketogenic diet. Dairy products are allowed, as are alcohols on occasion (aside from beer and sweet wines). The macro percentages remain the key factor in the success of this way of eating.

Who Is It Best For: Diabetics, obese persons, athletes (as Keto-adaptation can help athletic performance), and bodybuilders (see: Cyclical Ketogenic Diet).

Who Should Use Caution: Anyone who has a difficult time eating a LOT of fat.

Pros: A high fat diet knocks hunger on its arse. Weight loss can be fairly speedy without sacrificing muscle mass.

Cons: It is difficult for some to wrap their heads around eating so much fat and one may have a tough time adjusting so they are not eating too much protein. The first few days into this way of eating, some people experience "keto flu" as their bodies adjust.

More Information:
What You Should Know About The Low Carb Ketogenic Diet
Diet Doctor
Low Carb Ketogenic Diet Food List
Ketogenic Diet Resource

Overview: The Atkins Diet, created by the late Dr. Robert C. Atkins, is the granddaddy of all other low carb ways of eating. This way of eating allows animal protein, fats, low starch vegetables, limited dairy products and even some fruits (in the later stages). It does not allow bread, potatoes, sugar, legumes, pasta or starchy vegetables. The first two weeks of the diet, called the Induction Phase, are very low carb, with no more than 20 grams of carbohydrate allowed per day. Thereafter, in the Ongoing Weight Loss Phase (OWL), one introduces more carbohydrates into their diet each week until a level is achieved where one is still losing weight but not limiting as much as in the beginning. In Maintenance, the final of the phases, one increases carb intake to a level of weight homeostasis. There is no stipulation to eat grass fed, free range protein, nor to eliminate the intake of processed foods, including vegetable oils.

Who It Is Best For: Obese individuals (especially those just starting out in a low carb lifestyle) and diabetics.

Who Should Use Caution: Anyone who buys into the prepackaged foods put out by the Atkins company. These products, such as bars and shakes, are notorious for stalling weight loss on a low carb diet.

Pros: Great entry level introduction into the low carb lifestyle. Lowering carbohydrate intake can mean freedom from Type 2 Diabetes Mellitus and blood pressure medications.

Cons: The newer versions of The Atkins Diet push hard on selling the Atkins prepackaged foods. Though one would do well to acquire a copy of the 1972 version of Dr. Atkin's diet, as it dwells on more of the clean foundation of this way of eating, as long as the recommendation to eat soy products and vegetable oils  is ignored.

More Information: 
Atkins Diet – What to Expect
atkins.com