My mentor gave me an old list of about seventy breeds from "smartest" too "dumbest" which i think was compiled about five years ago from old force based trainers. The top five, in order were 1 border collie 2 standard poodle 3 german shepherd 4 Golden retriever 5 shetland sheepdog 6 lab.
Thought i might go up to six to avoid the (oh no, but labs are guide dogs!)
My club has found that using positive methods breeds long thought of as "dumb" are now winning titles! So, we have almost completely discarded the old chart, though nearly all would agree that the border collie is way up there. Also, some breeds arn't documented (such as the australian kelpie). In my opinion the kelpie is the smartest breed on average, they tend to works stuff out about three seconds before a border collie. But there will always be individuals.