I'm using Sold Gold Just a Wee Bit right now. I change every 6 months or so. I don't like to change often because I have sensitive stomachs here. They tend toward loose stools if anything is different. Still, I don't like to leave them on the same food forever, just in case they were missing something.
I like no-grain formulas (Solid Gold does contain grain though) IF they are not too high in protein. I do not like to feed any food that is over 32% protein. It can lead to pancreatitis over time and sometimes with just a feeding or two!! Larger dogs may be able to tolerate it better than yorkie-sized yorkies. No offense to any dog or person here but when you are comparing diets, I think it is more important to compare with dogs more the same size as yours. We have people with dogs from 1 pound to 25 pounds here -- obviously NOT the same situation! The smaller dogs do have a higher history of pancreatiits problems.
Merricks Before Grain is an excellent choice! If i can find it locally, I will switch to it next. I am trying to get our Hardware store where I buy my Solid Gold to stock it since they do stock other Merrick's products. I think it is one of the best choices around. Most of the no-grain products have too high a protein percentage for me to feel comfortable with. As a human with chronic pancreatitis, I am more conscious of it and never want my pups to feel what I feel with this horrible condition!