Every dog is different Ash and in reality there isn't a food that is perfect for all dogs cause if this was true then there wouldn't be hundreds of brands available. With that being said, Large dogs tend to be picky eaters period! They grow so fast and lots of things are happening rather quickly, mainly growing pains that dogs simply shut down to food for a few days at a time. One of the biggest mistakes though is that owners blame the dogs not liking there foods and go out to buy other brands. What this creates is another problem w/o most owners knowing. Now you've created a dog that is gonna be picky cause your giving him choices, and really dogs should not be giving a choice.
The reason dogs like cat food is simply cause it taste good to him, why is this? Cause of the simplicity of cat food and the higher protein that is in it. The way to reach a higher protein is by adding more meat, cats are true carnivores so there foods are manufactured that way especially a food like Natural Balance. Keep in mind, even though the ingredients might read the same and seem safe for your dog, its still cat food. It's manufactured and processed differently. The PH balance of a cat is different from a dog and oo much cat food can eventually lead to bladder/kidney stones and possible struvites crystallization in its urine.
You made a mention that you think your dog likes fish based foods, but you stated your feeding Nutro Large Breed w/Canidae LAMB can foods. Nothing near to anything fish base. I'm not surprise that he doesn't like the Nutro brand, its a rather bland food that utilizes way to much grains with very little meat in it. Remember dogs are carnivorous by nature yet that food uses within the first five ingredients 4 GRAINS. The first five ingredients in a dog food make up 50 - 70% of a food.
Here is the actual ingredient panel of the Nutro Natural Choice Large Breed: Chicken Meal, Ground Rice, Corn Gluten Meal, Wheat Flour, Rice Bran, Poultry Fat. Notice it uses Chicken Meal which is dehydrated chicken meat that is powderized, water is added to rehydrate back. Rice, Corn Gluten, Wheat and more rice is used - its a dog Ash not a bird we are feeding and all foods use a fat source and in this case they use Poultry fat which is any flying bird. So its not coincidence your dog doesn't like this food to eat.
You mentioned you found Taste of the Wild, they make 4 different meat bases. Its a grain free food so no grains are used at all. They make a Salmon based called Wild Pacific that you might want to try. You should purchase a small bag and go from there. Remember this food is one of a few foods that are rotational fed, dogs in the wild don't just hunt for rabbits all week and eat that. So this food offers 4 different line up of meats sources, they'd like for you to rotate and buy a different bag everytime you purchase. The foods are designed for that so you shouldn't encounter a loose stool issue but my suggestion would be to buy a small bag of each before and get your dog used to it.
Hopefully this helps, good luck with your dogs
STDT