It depends how long I won't be using it for. If it's a matter of hours then it goes to sleep. But if it's not going to be used for more than one day it gets shut down.
What will make our MBP's last longer?
Hmmm... I guess I should start doing one of those
What third option are you currently using?
I close all running apps (probably unnecessary, just habit), then shut the lid when I go to bed.