How would you rate Royal Canin dog food?

I have 5 year old yorkie pom and this is what we currently feed her. When we first adopted her we fed her Eukanuba but we switched to Royal Canin because i though it would be better coming directly from my vet and because its expensive at $75 per new bag. Apparently i was wrong because everyone keeps telling me that its not a very good brand because of some of its ingredients. They say that Blue Buffalo and Wellness are way better foods.