I don't know about dumb BREEDS.  I've met some dumb and smart individual birds from a lot of breeds. 
Though if I have to pick a breed, I think I'll go with Leghorn. 
Polish...well, if they can't see or react too well because of their crests then I don't count that as a dumb mark against them.  
...though there is a Polish rooster I know who thinks he's a cat.  No joke. He will come up and step on your shoes and rub his body against your legs and walk off again.  He also makes these weird noises that we think are him trying to purr.  He meows quite well!