I would think that alot depends on the snakes natural environment. For snakes, like BP's, that live mostly in the ground, and are primarily ambush predators, would have a more highly developed sense of heat detection and smell. Whereas arboreal and semi-arboreal species, that more actively hunt their prey in trees, or from low hanging branches, would have better vision. The fact that they are atracted to, and track motion, could make them seem more alert and intelligent. Ball Pythons, on the other hand, are just as alert, it's just that they don't have to move their head, because they can sense your location and movement because of their more prominent labial pits, which give them a 180 degree view.