Every dog I've encountered that was bought has been a great dog. All but one were extremely healthy and all were well behaved and very social.
Every shelter/stray dog I've encountered have had some trauma or hangup that made they way more trouble than I was willing to deal with. Current displeasure has been a "free to a happy home" that my parents got. This dog dislikes any guy with a voice deeper than Richard Simmons and if you're said guy and wearing a hat she's going to get bite-y.
Every cat I've ever known has been some form of asshole. Quite a few have been the type I approve of and enjoy. It hasn't mattered how they were acquired.