
I would hope no one would breed any crosses just for agility or any other sport. It's bad enough breeding designer dogs for the pet market
I would suggest you research the breeds you have mentioned & go to a few agility shows to see what dogs you like & then consider getting one for agiility as well as a pet
Shelties are very clever & quick to learn, but that is no reason to get one, just to win in agility-they should all be pets first wanted as companions who also do agility & not purely agility dogs