I have two labradors and I use Royal Canin - they make Labrador 30, a breed specific food. I also use Wellness brand canned food, and have been getting a small quantity of Taste of the Wild, a grain free food. IMHO, the extra $ you spend on more expensive food evens out in smaller portions and better health.
My brief experience with Science Diet was not good -none of the dogs "thrived" - their coats and skin were not good.
I've got 2 older labrador mixes and I use some of the newer "joint management" diets that are rich in glucosamine, chondroitin, and omega 3 fatty acids. It has done WONDERS for my older boys with some hip osteoarthritis.
Anecdotal, but here ya go: I recommend flax oil, 1 tablespoon per 100 pounds of body weight or so. I have arthritis in my hip (as well as elsewhere, no doubt, after a 50 year athletic career). A few months ago, on advice of a couple of friends, I went from taking capsule type supplements to a much higher quantity of flax oil per day. It is supposed to be good for the critters as well, so I added it to the dog and cat diets.
Anyone who has seen a picture of my huge maine coon cat, posted in one of the "defense against dogs" threads, remembers his size - about 24 pounds of kitty. At 13 years old, he has arthritis in his front legs and paws. He has been on glucosamine/chondrotin as well as dieted down to 20 pounds, and that was controlling it. He was far less mobile, however - for example, he would go up and down the stairs perhaps once a month.
Within a week or so of starting the flax oil, the cat is completely different - goes up and down the stairs several times
daily, hops up and down from chairs rather than asking for help, etc. Really a striking change.
For all with older or arthritic critters, I think it is worth a look.