I'll keep my reply to people whom I have had first hand interactions.
Drummers: In conversation, both Vinnie Colaiuta and Jojo Mayer made HUGE impressions on me as being SUPER intelligent. Tony Williams was a very smart person. Mark Gulianna and Tyshawn Sorey are both brilliant young men. John Riley is not only a wonderful teacher but a very intelligent man, the same could be said for Gary Chaffee.
Other musicians: Wayne Shorter is a terribly brilliant person, however his brilliance is often obscured in his "non-linear communication" processes. The same could probably be said about Cecil Taylor (although that is not a first hand claim.) Jackie McLean and Andrew Hill were both VERY smart men. Herbie Hancock and Chick Corea are very smart individuals, and so is saxophonist Steve Coleman. And pianist Vijay Iyer is clearly operating on a different level.
My assertions-opinions are based on interacting with these people and being struck with their high-level communication skills. The amount and variance of subjects that they referenced in general communication, vocabulary, accuracy, and the clarity in which they communicated was also clearly evident in our interactions.