It takes Willie so long to go through a bag, that I change every bag or two for sure.....no set kinds.....He will eat anything, and he seems to like when we change and he eats better....With him, it's like he gets bored with it and hardly eats at his twice a day feedings, so switching helps him.....he is lean enough.....LOL.....Right now we are on the end of the bag of CORE (finally) and going to California Natural, Herring and Sweet Potato.
Sasha is the same way. I used to feed her Solid Gold, but after awhile she would eat very little, sometimes even going a day without eating! I switched her to Natural Balance which helped a lot. She loved the different flavor. Right now, she's currently on the Venison & Sweet Potato formula and she loves it! She's gets a little bit of canned mixed in as well for a little enticement....spoiled baby I plan on trying a few other brands as well once she goes through all the flavors. I know for sure I'm going to try Wellness, but I'm not sure what else yet.