I've said this before, but since we're on the subject, for me, Cariou played the character as the "Ballad of Sweeney Todd" lyrics describe him: "Inconspicuous," "quick," "quiet," "clean," "smooth," "subtle," "a perfect machine." Cariou had a brooding quality, with an element that he could explode at any second. When he finally did, at "Epiphany," and came to the edge of the stage, even in the enormous Uris Theatre, you wanted to draw back from him. It was really terrifying. Hearn is terrific in his own right, but for me, he's really playing the madness from very early on. He seems contemptuous of Anthony in the very first scene, and when reunited with his razors in "My Friends" is screaming in the street. For me, it differs in the concept of a "quiet subtle perfect machine" of a man who has been plotting revenge for 15 years. So, the payoff felt greater to me with Cariou, but Hearn gives such a committed performance, I don't begrudge anyone who has a preference for him in the role.
Begin at the beginning and go on till you come to the end: then stop.