My first dog was an 8 year old cocker spaniel from the local humane society. He came with hearing issues that were progressive to the point that within a year he was deaf, I worked from day one with teaching him hand signals for obedience so when it came time we would still be able to communicate and he picked it up extremely fast. He bonded to me right from the start, ran right into my lap at the initial meeting and wouldn't leave. He was my constant shadow for the 3 years we got to spend together and I miss him dearly. When I left for work he would literally sleep in front of the door without moving for the entire time so he wouldn't miss when I got home. He did this up until the day I had to put him down due to a severe ear infection we weren't able to treat and he was in pain. Even in pain he was loving and never once was grumpy with me, he was a real trooper.
Shelter dogs, especially those who are over a year old are easily screened through a reputable rescue or shelter. Those who make it up for adoption have been through intensive scrutiny towards guarding, aggression, trainability, and health issues just to start. What you see is what you get, if a dog can survive in a shelter with little human interaction, food, exercise, etc. and still be happy and up for adoption then you have a pretty steady dog. Not all dogs are perfect, every dog has their quirks and you need to know what you can deal with and what you can't. Just like with a breeder, be very honest with yourself and with the staff and they should be able to match you with a good dog.
Personally I don't have a problem looking at either reputable breeders or rescues, they both can have amazing dogs which will be a good addition to a family.
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010