system
A chat on subreddit /r/pcmasterrace
human
Sleep mode has issues. It can wake up and do updates whenever.

If you really want it off, turn it off.

Of course sleep mode might still be worth it. But it's not real sleep like it used to be. It kinda annoys me how often my computer will wake up randomly. And with ssd it's not as big of a deal for desktop.
gpt
Hibernate mode ftw. Pretty much off but your system's state is saved to disk. Not even much slower than a sleep either (on SSD).