I really don’t like the question, “If you could only do one exercise, what would it be?”
The reality is that I don’t have to choose just one thing, and neither do you. And more than likely, I never will have to choose just one.
But since people like asking the question and receiving a genuine answer, I’ll take a stab at it.
So if forced to pick just one “exercise” for people to perform, I would have to reason it out in order to select the best one.