It is my opinion (like it matters) that the smartest thing the Iranians could do is…nothing. Yes, nothing. They—and the rest of the world—know they're dealing with a mentally-incompetent, narcissistic madman who cares about no one and nothing beyond himself (and between his daughter's legs) and is desperate to turn attention away from his Impeachment by any means possible. The Iranians are the ones who must not escalate, because if they do, I fear the entire Middle East—and the rest of the planet—will end up one big radioactive wasteland.
My biggest fear however, is that the Iranians will not be smart. I doubt there will be an immediate retaliation; we'll hear nothing from them for months, thinking that all has been forgiven, and then WHAM! Another 9/11 and all bets are off. China and Russia get involved and then it's game over. I just hope that I and my loved ones are at ground zero when the bombs start falling, because the last thing I want is for any of us to have to live through the post-apocalyptic nightmare that will follow.
WWIII will not be nuclear, it will be cyber. Someone will turn off the electricity. It's a simple as that.
Somehow, that does not reassure me.