Both Wellness and Merrick's are considered 5 star dog food according to this site:
http://www.dogfoodanalysis.com/
The brands that I usually rotate for both my cats and dog are Innova, Innova Evo, Orijen, Wellness and Merricks and I find they do well on it.
I have a Devon Rex kitty and she use to have really bad eye gunk and waxy ear buildup. Since I've switched to grain-free food, her ears rarely need to be cleaned and her eyes are less gunky. AND, the litter box is less stinky (or am I just getting use to the smell... lol)