KDE Plasma is pretty good, I used to hate it but now I use it all the time

No, because every environment has different concepts. It is really hard to decide. You just have to try things out intensively and see to what you want to stick.

not really. as long as they are not resource intensive and usuable, i pick any over the other

KDE

No. I recommend quiet environment everywhere.

I don't use one myself, but if I had to choose one, I'd use KDE!

I'm a fan of KDE

i don't use DEs

KDE. It's clean, it's fast and it's useful. Also KDE connect is one of the best phone integration apps.

My recommendation depends on the context in which your friend is asking. In the absence of context... KDE is great!

My favourite desktop environment is made of solid oak wood.

I use i3 at work, where I really want to solely focus on the apps themselves, and XFCE at home where I prefer a more classic desktop