A couple years ago, I rescued a 1 year old pointer mix from a shelter.
She had severe behavior problems due to a life of roaming the Kentucky countryside, but my wife & I were against giving her back to the shelter.
We went to several obedience classes & found that she just couldn't be around most other dogs, without a total meltdown.
I don't know what it is, but she just dislikes most other dogs.
Since we were having such a hard time with her, I decided to get a DNA test done by a reputable lab.
Well...My pointer mix turned out to be an American Foxhound/Neopolitan Mastiff/Shar Pei mix.
Now, I see that her listening problems come from being an independent foxhound, her aggression comes from the shar pei & her sleep habits/laziness come from the mastiff.
This is the long way around to answering, but my dog has turned out great.
She's now over 3 years old & has matured, drastically.
I have a 8 month-old son & she loves him, dearly...I couldn't ask for a better buddy, for him.
If you have children, a shelter dog may not be the right fit...Just choose wisely & think very, very hard on it, before you decide what dog to get & where to adopt from.