Choosing food for your dog or cat is probably the most important decision you'll make as a pet owner. To complicate matters, the options are seemingly endless. While I'm not a vet or a nutritionist, I do have a background in the sciences and as a direct result of owning a dog with allergies, I've spent a significant amount of time researching all the options out there. Oh, and in case you're worried about taking advice from a for-profit company - my company doesn't make pet food, nor is it affiliated in any way with any companies that do. So here's the distilled version of what I've learned along the way. Hopefully you find it helpful.
Your first decision when selecting a pet food is to decide if you'll go the traditional route, with a cooked diet (including canned wet food or dry kibble) or jump on the raw food bandwagon.
The argument in favor of a raw food diet for dogs and cats is simple - raw food is the format closest to what your pet has evolved to best utilize. Additionally, the argument goes that cooked food looses much of it's nutritional value as a direct result of the cooking process, especially when it comes to bioactive enzymes and the like. Unfortunately, there are no conclusive studies comparing raw and cooked diets, so you'll have to decide for yourself.
I'm a strong supporter of the argument in favor of a raw diet, mostly because it seems highly logical, but also due to my own experience feeding kibble as well as a raw diet to my dog and comparing the results.
If the decision were left up to my dog, the choice would be clear - raw all the way. There's no questions that he favors any raw food over any kibble.
Although not exactly scientific, I've also applied my own senses toward answering this question. Raw food, to me at least, smells and looks very healthy. Kibble, on the other hand, smells and looks disgusting.
I've had my dog on a raw food diet for over a year now. I don't give him any supplements (no fish oil or the like). The results? Remarkable, in my opinion, and clearly in the opinion of other folks we come across on our daily walks. My dogs coat is, frankly, perfect. His teeth are very clean. His breath - not so bad! I honestly get an overwhelming number of complements from vets as well as folks on the street with regard to how healthy my dog looks.
Finally, the most disgusting, but also the most informative test when it comes to food quality - the stool. When on a kibble diet, my dogs stool was dark, voluminous, irregular (routinely mushy), and very stinky. On a raw diet, his stool has been light, noticeably smaller in size, highly regular (very firm), and has very little odor. This, to me, is how a dogs stool should be, and is the clearest indicator that I've made the right choice in going with a raw diet for my pet.
On average, a raw diet will be noticeably more expensive than a kibble diet. You could look to spend less by preparing your own homemade raw diet, but for most of us, the savings would be minimal and the level of effort required would be high. A raw diet still needs to be balanced, containing a biologically appropriate mix of meat, organs, and bone, to provide proper nutrition.
Sine it's cooked, kibble and canned wet food is easier to store and serve when compared to raw diets. Typical raw diets must be stored frozen and thawed within a day or two of use. This means you have to plan ahead. Don't be too discouraged, though, as its not a huge deal once you get into the habit of it and if you ever forget, you can do a rapid thaw of a frozen raw food by soaking it in warm water.
Kibble is a lot easier to travel with since it can be stored at room temp. At the same time, there are freeze-dried versions of raw diets that are pricey but very easy to travel with and prepare on the road.
Perhaps the most often cited argument against a raw diet is the risk of bacterial contamination and food-borne illness. I don't think this argument holds water, though. Why? First, there have been plenty of recalls regarding salmonella and the like in cooked kibble and canned wet foods over the years. They're clearly not immune to this risk. Additionally, a pets digestive tract is more capable of handling bacteria than is the human digestive tract, so we shouldn't carry our own concerns over eating raw meats onto our dogs. We're different.
Lastly, there's a technology available (and growing in popularity) that can significantly reduce the likelihood of bacterial contamination in raw food without undermining its nutritional value. The technology is called high pressure processing (HPP), and as the name implies, it uses a very high pressure environment (not heat) to eliminate most microorganisms. Some hardcore raw feeders may scoff at this technology, but in my estimate, it's a very reasonable, practical, and smart compromise. While a dog can handle far more in the way of bacterial contamination of food than we humans can, at a certain point, even a dog will succumb to food poisoning. You also can't ignore that we live right alongside our pets, and even levels of bacteria our cats and dogs might be able to handle could pose a risk to us and our family members. Many commercially prepared raw diets made from poultry (chicken and turkey) already use high pressure processing. At least one company (Nature's Variety) has extended this technology to all their raw diets.
Sheesh - that was a lot to get through to answer the first question. Luckily, this second one is a no brain-er.
In general, the composition of dog food will follow either a conventional model, including relatively highly proportions of grains and vegetables and low proportions of meat, or what's often referred to as the prey model, which contains 80 to 95% meat, organs, and bones and very low proportions of vegetables/fruits and little to no grains. All raw diets I know of follow a prey model, so this choice is effectively made for you. It's always good to check, though.
If you're opting for kibble, find one that follows the prey model. The evidence on this is crystal clear. At best, grains are a filler for dogs and cats, providing little to no nutritional value. At worst, they may be harmful.
At this point in the discussion, you should be resolved to either a prey model raw diet or a prey model kibble diet. Either way, you've eliminated a large number of the options out there, and narrowed your selection nicely. Consider the following when making your final selection.
Any commercial producer of significant size is likely to have had a recall or two along the way. There's only so much that can be done to prevent contamination and eventually every company will get hit. But before buying a particular brand of food, check out the list of recent recalls at FDA.gov. Keep in mind that larger companies will naturally have a larger number of recalls, but at least make sure the brand you're considering hasn't had an overwhelming number of recalls that may indicate something more than bad luck. There's no fool-proof way to discover which companies truly value quality and which do not, so use your gut.
Lets be frank here - this is dog food, not rocket science. If you feel like you need to go get a PhD in chemistry before you can understand a particular brands ingredient list, move on. There are plenty of options out there with very straight-forward and easy to understand ingredient lists. Reward these companies for their efforts and favor their products.
Another no brain-er - your dog or cat needs a variety of protein sources. Most food allergies in pets are acquired over time. Meaning if you constantly feed your pet a chicken based food for years on end, it's far more likely that he or she will develop an allergy to chicken. This is a well documented fact, so find a brand that's readily available in a wide variety of meat sources (a fish variety, poultry variety, beef variety, and preferably a few exotics like venison, rabbit, etc.). Every couple of weeks or months, switch up the major protein source. Your pet will likely appreciate this variety, too, and be healthier for it.
If you select a high quality food and your pet is otherwise healthy, there should be no need for supplements. Save your money and put it towards a better food or use it to buy a natural chew that can provide some natural supplementation (like raw bones and antler chews). Don't buy into the latest fad...life bits, joint support, life stages, etc. These are predominantly marketing ploys, and even though the food may be otherwise decent, I'm a strong proponent of using customer choice to discourage companies from playing marketing games.
In my experience, the quickest and most fool-proof way of evaluating the quality of what's going into your dog is to evaluate what's coming out the other end. Yes, it's a bit gross, but other signs of diet quality take a significant amount of time to develop. It can take weeks or months of being on an improved diet before improvements are seen in skin, teeth, and coat. A good diet will routinely produce a relatively small, very firm stool with low odor. An added benefit to an improved diet - no more scraping mushy, stinky dog poo off the lawn!
Put in the most concise form - I'm convinced that a prey model raw diet, treated with high pressure processing, is best for most dogs, cats, and humans, but not so great for ones wallet. Particularly for those with multiple pets, a high quality raw diet may, understandably, be out of reach. Your next best option is a prey model kibble diet (at least 80% meats, organs, and bones), preferably grain-free. There are many good options in either category, just be sure to rotate amongst various protein sources and reward the companies that provide straight-forward ingredient lists and shy away from marketing gimmicks.
For over a year now, I've had him on Nature's Variety Instinct Raw Frozen Diets. It's readily available in most pet stores, is one of the more affordable raw diets, and all varieties get treated with high pressure processing. Again, I have no affiliation with this company, apart from being a customer, and have no expectation of any gain as a result of this recommendation (though I wouldn't mind a coupon or two).