Windows-like icons, or real icons?

[PonyRoleplayer]

Something that always wondered is whether windows-like icons for apps is better than the real icons from that era. In my case, I see all LibreOffice icons are replaced by Office icons, and while it helps to give a Window-esque vibe, it also kind of lies in a way to the user. Same with Thunderbird that has an outlook icon.

So I want to ask you guys. What do you guys prefer? Windows fake app icons, or period-accurate icons for the apps?

To give you an example, this is what old thunderbird icon looked like: