I feed Orijen 6 Fish to my two Dachshunds. I've been feeding it for about two years and couldn't be happier with it.
As for "why?" there are two primary reasons. First and foremost, my dogs have done extremely well on it, better than on any of the other dozen or so foods I have tried (and I have tried everything over the years from garbage like IAMS, Science Diet, and Purina, to middle-quality food like Blue Buffalo, to high-quality foods like Canidae, Taste of the Wild, EVO, and Innova). They have shinier coats, more energy and stamina, very healthy skin (which was not the case with some other brands - my black dog used to have terrible dandruff, and they were both always itchy! This food cleared ALL of their skin problems up in a matter of weeks). They also love, LOVE the taste, which is always a big plus. Their stools are small and firm with this food, and they only "go" about once per day.
The other reason I like this food is the confidence I can have in the types of ingredients used. It's completely grain-free, and completely filler-free. It's also guaranteed to contain at least 70% meat (All human-grade, unlike the "4D meat" found in a lot of kibble). It's high in quality animal protein and low in carbohydrates. I can also have confidence in the quality of the ingredients (all human-quality and caught/ranched/grown/produced/packaged in Canada, not China).