General rule- the best food you can feed your dog is a raw diet (raw food, e.g., Primal, Small Batch, Stella and Chewy's, Origen raw, K9 natural, etc). This is balanced and complete with muscle meat, organs, ground bone, a small % of veggies and fruit and additional minerals and vitamins. Typically 40% - 95% protein, with the lower % for freeze dried options. Tons of benefits but can be pricey, especially for a larger dog.
After that, it's a question of what kibble or canned food you want to use. There are a lot of brands at a lot of price points so a few watchouts. There are 3 general steps- 1. quality of the starch binder, 2. quality of the meat and 3. quantity of the meat. And of course, what price point fits in with your budget.
All kibble need some starch (in the form of grain, beans, veggies, etc) to make the meat into kibble form. Some dogs can't process various starches. Grain and corn seem common allergies, some dogs are allergic to soy or tapocia and a few are allergic to potato. I have yet to see a dog allergic to legumes (chickpeas, lentils, etc).
All ingredient panels are listed in order of weight before the mixing and cooking process so a higher quality kibble should have meat or a meal as the first and second and maybe third ingredients (e.g., chicken or chicken meal, duck meal, salmon, beef, lamb meal, fish meal). Chicken, beef, duck meal is just cooked meat and bones ground up which is fine as this is quality controlled. Unspecified By-product (e.g., by product versus poultry by product) can be dangerous since you don't know what animals are in there (roadkill?, diseased animals).
Lastly, you'll see a Guaranteed Analysis panel that lists % protein, fat, fiber and moisture. Kibble will range from 20(ish)% to 35(ish)% protein. You generally want a higher % protein (dogs eat meat and not starch) although some would argue that kidney compromised dogs would benefit from a low % protein diet. A high % protein rating plus lots of meat listed first in the ingredient panel means your protein is coming from meat products versus other sources (corn gluten, etc).
You may be tempted to calculate cost per pound of kibble but a more accurate calculation is cost per feeding since the same sized dog can have different recommended feeding guidelines. Pain in the butt to do. Generally higher quality kibble will need to you feed less to get the same nutrition.
Every dog is different and their dietary requirements will change over time. What works for one person may not work for you therefore there isn't really a "best". And most people will do a mix of feedings (e.g., kibble plus raw, kibble only, canned only, etc). At the end of the day, the fact that you care and make thoughtful decisions means you can't do wrong by your pet. Dogfood Advisor website is a good resource.
My 60lb foster pitty gets a high quality kibble, plus supplements with raw frozen meats, chicken or turkey parts, marrow bones, raw veggies and fun things like coconut oil. The last 2 fosters have gotten this diet and have made dramatic improvements which was necessary as they were straight from the shelter where they got supermarket quality kibble/Walmart kibble and did not do as well as others on that food.
Hope you find this helpful. =)