I'm using Avast Free
I'm not sure but probably the latest version. I just installed Avast yesterday from the avast.com
I just installed Windows 10 Pro 1709 yesterday. OS Build 16299.1087
I got no other security related software installed other than Windows Defender that came with Windows 10.
I've used BitDefender before, but this is a fresh install of Windows 10 so no history of other AVs other than Windows Defender was installed right now.