I have been taking Nessa to the puppy classses at PetCo and have been very happy with them. It is always going to depend upon the specific trainer leading the class but we have had good luck. We started when Nessa was about 10 weeks old because I really wanted her to be well socialized. As someone else said, the physical set up is not ideal but I just want to learn the obedience techniques to work with her at home.
I had looked into another obedience trainer but the price was much higher ($150) and there wasn't any puppy play time. Also I would have to wait several weeks for the class to start and I didn't want to wait.