6. Border Collie
Smart and impossible to wear out, border collies are arguably the best athletes in the dog world. These midsize dogs tend to dominate in canine sports like agility and Frisbee, and are always — always — atop the list of smartest breeds.
Weight: 30-45 lbs.
Best Qualities: Loyalty and boundless energy. Their hyper-intelligence also makes border collies easy to train.
Drawbacks: This is not a dog you can leave alone all day. The border collie was bred to herd sheep for hours at a time, and that work ethic cannot be turned off. They also get bored easily, so you need to challenge them constantly, which is why they’re great for learning tricks.
What to Do With Them: Border collies have a natural instinct to nip at things — that’s how they get obstinate sheep to cooperate — and some will nip (but not bite) at bike tires, or even small children who seem to be running astray. Thus they’re not the best dogs for mountain bikers, skateboarders, or parents of young children.