I don't really like when people try to compare one animal's intelligence to another. For instance in the dog world these three dogs are considered smartest because they will learn and perform the most tricks over and over: Border Collie, German Shepherd, Standard Poodle. Meanwhile the independent chow chow is considered "dull" because he won't fetch a ball twenty times in a row. If it were up to me, I'd consider the chow smarter than the rest of them because he is smart enough to realize there is no point in bringing a ball to his master if the ball is just going to get thrown again. He may love his master just as much as the other dogs do theirs, but he sees how illogical it is so he stops. Why should he waste his time doing something so pointless? The other dogs don't think for themselves; if their master says "Fetch!" they do it without thought.
But that is just me. I think people confuse "trainability" with "intelligence" when really, the most intelligent creatures tend to be the most independent, and therefore the least trainable.
(That said, some chickens have definitely retained more instincts than others. If I had to pick I would say a breed that looked out for predators, foraged well and went broody often would be more intelligent than one that could not do those things.)