I shut it down. It bugs me when something is kept running overnight. Plus, I live in a very old building with funky wiring. If my machine is going to go "pfoof," I'd rather it take place during daylight hours.
I turn my computer to sleep at night instead of turning off, but I usually also disconnect power cord. It is powered from battery when it sleeps.
My iMac and Lenovo (Ubuntu) laptop are turned off when not in use, which is usually overnight. My Asus tablet and Chromebook are in sleep mode when not in use and are not turned off. They are only attached to the mains when being recharged.