Chrome OS fave. Love my HP chromebook :D although, is not as good as my former Toshiba 2 chromebook.
Which computer operating system are you using? and which is your favourite?
I'm using Arch Linux and it's my favorite.
Just Windows 10 here, Im not sure what my favorite is ive probably yet to find out.
I'm using Windows 10. I don't have a favourite really!
Using OS X El Capitan. It is my favorite by far. I use Windows for gaming and some other Windows-exclusive programs, but I much prefer OS X (or now, macOS).
Linux
Windows 10. It's my computer's default.
My gaming PC still has Windows 7 on it as it's more compatible to some older games and takes the beta-test games better. My other PC has Windows 10 and they are both good set-ups in their own ways.