I havent formally trained my yorkie yet - hes only 4 months
(although i do work with him at home)
I have trained my german shepherd, i have experience with a few private schools in my area, petsmart and i did have a private trainer come to my home every week for a summer.
I find that for the money, i got the most out of the private trainer. She was only about $50 more than petsmart or the private school and all her attention was focused on ME and mine. She really spent the time teaching me how to train, which is incredibly important imho. I think that if you are a serious trainer, you need to know how to handle your dog/s and how to teach them to learn. Training is an ongoing process, not something you go to class for and then forget about the rest of the time.
I would suggest maybe looking into something like this before working with petsmart. They are great to get your Canine Good Citizenship papers for therapy work or rescue work.