Okay I will speak for the pure breds first, the major advantage is that you know pretty much what you are getting. The size, tempearment, coat length, grooming requirements, potential health problems, etc. You can adopt an adult from a breed specific rescue. Often breed specific rescues are much more stringent in their temperament testing than your local SPCA. SPCAs do much good, but I often think they try to move animals so as to avoid putting them to sleep, thus animals who have problems or are not yet ready for adoption are pushed onto unsuspecting folks. Breed specific rescues will interview you and determine if you and the dog are matched, they don’t want to get the dog back because of incompatibility. You are again saving a life, just from a different source.
Now for mutts or SPCA type rescues. 2 of the 3 dogs I have owned since moving to Australia have been rescued from the pound. Both were on death row with limited time left. Both were wonderful dogs, but I am a dog trainer, I know what I am looking at and am not swayed by cuteness or emotional attachment.
So both are good but if you go the SPCA or similar association route, take your time, sit with the dog and observe its behavior, its interaction with other dogs and people. You don’t want one that is too shy (could become a fear biter) or to rambunctious because they can drive you crazy. Just use common sense. And I think you are smart to be looking for an adult, pups are cute but as demanding as a baby.
Dogs are the best friend you will ever have. I literally cannot imagine living without one so I think you should definitely get one! Keep us posted.