As some of you know, I volunteer for a rescue and I think our organization is great. Maybe I'm a little biased
but I have to tell you that some rescues are not that great. We have worked with other rescue groups and some of them are amazing and some of them I would not touch them with a 10 foot pole. Also personally before I started volunteering I found some pretty horrible rescues.
From my experience of being a volunteer, a rescue should work with you and get to know you and what type of dog will work with you and your family. A good rescue should be true to the dogs and be fully honest and disclose everything to a potential adopter about the dog. They should be professional and courteous, responsive and knowledgeable. One time I declined someone to adopt from us because we felt they weren't appropriate for rescue. I told them that and they actually thanked me and appreciated my honesty. They should not rush you into adopting a dog or push your decision in anyway. I also think that a good rescue continues the relationship even after the adoption. Followup and make sure that things are going well and provide advice and training whenever necessary. A good rescue will make sure that if the adoption doesn't work that the dog gets returned to them. These are just few of the things I think make up a good rescue. There is way way more things.
Some people prefer to adopt from a rescue instead of the Spca. Rescues work differently than the Spca does.
Wherever you adopt your dog from. Just make sure that you do the research and you are comfortable with who your dealing with. It never hurts to get a good referral too!