Both parents are on openSUSE KDE. They only use the web browser and printer, so it pretty much doesn't matter what UI they use, but it really helped with their acceptance that KDE not only works similar to Windows, it was a clear upgrade from Windows 7, with it looking more modern and being a lot faster.

I also like openSUSE for this, because YaST allows me to administer their PC without cracking out the terminal for everything. It just gives them at least a tiny bit of hope that they might be able to do this themselves. And my brother, who's not a Linux person, has managed to fix things via YaST without my help.

Ultimately, though, I use openSUSE KDE myself, and that's really important.
If my parents mildly complain about something, I can proactively offer to change that, because I know all the settings of KDE and YaST.
Or if I don't know whether there's a setting, I can go digging for it on my system.

But perhaps most importantly: "This Linux thing isn't working." – "Hmm, it's working on my system, so there's gotta be a way to fix it."
That immediately shuts down any negativity, so I can concentrate on fixing it, rather than deflecting their grumbling.