It depends on what type you are and what skills you have. If you're a young leading man type who plays romance well, then you'd obviously want to be Chris. If you're more of a character actor or interested in not being the typical young lead, then go for The Engineer. But ultimately, you should read/listen to/get to know the show and she which you relate to more and feel drawn to. Its kind of silly to choose a role based only on the size and in my experience, you will be more successful in the role if you connect with it.
“I regard the theatre as the greatest of all art forms, the most immediate way in which a human being can share with another the sense of what it is to be a human being.”
``oscar wilde``