I'd play Smith. I know Ryan has been all the rage, but I have never been that impressed with him. He is a B-lister. Going up against a motivated Steelers defense is going to be tough. This is Smith's chance to show that he belongs. Seattle's defense is much more suspect. My gut says Smith.
I'd go with the Cards defense. It's Bradford's first game. There should be some culture shock. Their WRs are suspect, plus Mark Clayton doesn't even know the offense yet. Cardinals will blitz often and try to stack the box against S-Jax.