Most shelties are very smart. It's just a very intelligent breed, in general. My grandmother's shelties showed me that at a young age.
So, get a clever one, plus make them exceptionally handsome/pretty, add a cup of cuteness to the recipe, and you've got a winning combination!
Yes, I have had plenty of cats that were calm and happy all the time...until a visitor came around. You're right, they are both beautiful cats.
Love All Life, Thank You For Posting! :)