Mutts. Oh, sorry; "mixed breed". They tend to seem to be a bit more intelligent and hardy and avoid many of the health deficiencies that are bred into highly restricted blood lines (looking at you, snout-less dogs and you, cavaliers with your too-small brain case).
My favorite so far was a breed of one. A Kelpie-Aussie mix that came from a working stock breeder upstate. Amazingly intelligent, loyal, athletic...but still loved to lounge when appropriate. Not quite as intense or hyper as a Border Collie. Wonderfully protective of the children. My spouse was working at a service dog organization when that dog was a puppy so she had the benefit of 8 hrs of daily training and she *loved* to have a job to do. She also didn't have any of the obvious signs of hierarchy-ness that so many dogs display; rather she acknowledged that yes, we were in charge but it was very clear that we were *partners*, too. I get..disturbed by dogs that simper, and strongly dislike those that are aggressive, so she was perfect.
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“For small creatures such as we the vastness is bearable only through love.”
―Carl Sagan