How can you even say "breed"? I have a mutt, black lab and chow mix that could make most peoples head spin on intellegence. Don't discount mutts... I have worked with many dogs and other types of animals and you can't really specify what breed or mutt dog is smarter. This whole thread is kinda stupid. It all boils down to the dog, the owner/trainer and enviornment along with a few other things.
My dog, again is a mutt, but has been in several shows across the country, published in various media, has been on t.v. and now is just living the simple life, and living it well.
All dogs have potential, and to disregard some is just hurtful. Some have better instincts on certain things than others, but the same can go for humans too.