The general design goal is to optimize the tubes (diameter, wall, number, arrangement) for heat transfer, choosing a material that is sufficiently corrosion-resistant while compromising thermal efficiency as little as possible. In clean shell side environments you can enhance heat transfer with finned tubes.
But rather than repeat what others have done, start by asking what is the current industry standard.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."