Smarter?
Hmmm...I guess I'd have to say that neither of them are very smart...
If we're judging them by which are hardest to catch, then...
It's true that salmon are a little further along the evolutionary road than are steelhead, as Salmo pointed out. However, pink salmon are the fartherst along that road, and they happen to be just about the easiest one to catch.
I guess that's not the answer.
I've caught the same fish twice in a day, steelhead, chinook, and coho. Using broken leaders/lures as the evidence, it's taken a bit for the salmon, but I did once catch the same steelhead in two straight casts, a hatchery summer run in May of 2000.
That doesn't sound too bright for either type.
I've had days where I've caught coho after coho, king after king, and steelhead after steelhead...and days when I could sight fish hundreds of each and not hook any, or at least not very many.
I've watched fish after fish of both types refuse my best presented baits and lures, while I've had some of each hit things that any self-respecting fish would be embarrassed to even acknowledge, much less eat.
I think it's not very accurate to put a human measurement of "intelligence" on animals, at least ones that do indeed have brains the size of peas.
My opinion falls somewhere along the line that it is more proper to measure the ability of the fisherman to figure out what works best at a given time during given conditions. When a river is perfect steelhead green and is full of fresh fish, almost anyone can catch at least one. A week later as the river has dropped way down and no fresh fish have arrived, only a few are caught.
Did the fish get "smarter"? I doubt it. They still respond to the same stimuli and react with the same instincts.
Did the fishermen get "dumber"? Of course not...but the conditions changed and their technique did not.
I do, however, find it notable that during those perfect conditions where everyone caught a fish, a few guys caught more than a few...maybe a lot more than a few.
More importantly, I find it more notable that as the conditions get crappier, they're the same ones who catch the few that do get caught.
I guess my 'final answer' is not an answer at all, but a comment that there probably isn't a real answer.
Fish on...
Todd.
_________________________

Team Flying Super Ditch Pickle