lisaz,

I've never heard about rotating foods before but I know that puppies are supposed to have especially sensitive stomachs so it probably wouldn't be a good idea to have a puppy switching foods. I would ask your vet who probably would have some good advice, especially if they know your dog well.
I've always heard that dogs appreciate a stable diet, so if you are considering rotating it should probably be done gradually.
It's also hard to know which brand to choose- it seems like there are problems with most major brands. I used to feed my dogs Nutro (when you look at the label it seems to have the least amount of by-products) but one of my dogs developed crystals in her urine and the vet suggested I switch to science diet. I was hesitant at first since I've heard bad things about Science diet, too, but I made the switch over a year ago and both my dogs are doing well on it. Hope that helps!

Pembroke_Corgi