As far as Petsmart classes, I started my GSD in puppy classes at Petco, BUT my trainer there is a professional (she formerly had her own training center before she moved here) and her breed is Dobermans. And she LOVES my dog.
It will only go so far, though, and we will be moving to a more formal class with the kennel club next month, with my current trainer's full blessings and encouragement.
One of my classmates at Petco told me that she had started at Petsmart, but left there because the trainer was clueless.
It all depends on the trainer, whether at a pet store, kennel club, or other venue. Ask other dog owners in your area where they train.