Smarter than what? Or compared to what? What does the test look like? Ability to not get caught by you?

Salmon are slightly more evolved than steelhead, so maybe they should have the evolutionary edge in intelligence. Intelligence is usually measured as a function of reasoning ability, but I suppose it could be rated otherwise. Neither species shows much, if any, capacity for reason. It seems their behavior depends mostly on instinct (archtypal) and reaction to stimuli. Both will bite a hook dressed with a piece of yarn. Not too bright.

As far as relative ease of catching, it depends. Steelhead have the longer freshwater life history and tend to revert to troutiness the longer they stay in freshwater as adults. Salmon generally exhibit less feeding behavior after re-entering freshwater, which probably explains why you can get skunked after pounding a pool you know contains a couple hundred salmon and a successful day of steelhead fishing is likely if there is at least one fish in the pool you're fishing.

If smart applies to catching either of these fish, it is the relative "smartness" of the angler that counts.

Sincerely,

Salmo g.