I'm pretty bias. All my dogs I've had, since I moved out from my parents, have been rescues. Many of which were special needs but I knew that going into it. In many cases your mixed breeds are healthier than pure bred.
Rescues usually have dogs looked at by a vet before they are adopted out. Any good rescue will let you know of any health issues. Having a puppy from a good breeder does not guarantee that there won't be health issues. Sometimes the odds are just against them.
Just find a dog you really like and one that works for you. Once you adopt you can have your vet check him out. Most of the time he'll be just fine.
I tend to end up with the sick ones no one wants. There are way fewer sick dogs out there than healthy, active mutts.

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