It may be the question that I am asked most frequently... should I do group or private training for my dog? My answer is, it is entirely up to you based on what you are wishing to accomplish. Let me explain this a little further.
If you are looking to do some basic training and your dog has minimal experience being around other dogs, maybe even has some issues (such as fear or aggression) towards other dogs or people, or has no issues at all with other dogs or people but you want to work on your relationship, I would recommend doing a group class first and if additional training is needed to address the specific behavior issues, we could do follow-up private lessons.
Whereas if you are a person that needs a lot of one on one instruction or your dog has purely behavior or environmental issues and their obedience is fine, a private lesson plan is probably a better way to go.
Neither way is the "right" or "wrong" way, despite what some may say. You have to pick the training that is going to suite you and your dog the best in order for you to get the most out of it.
For me, I love both. There is nothing better than watching a class grow together, help one another and even learn from each others dogs. At the same time, little beats meeting a dog and owner pair and assessing the issues and creating a customized training plan just for them. When you work that closely, you get to see the relationship take shape much more intensely and that is a huge reward as well.