Check out https://blog.martin-graesslin.com/blog/2018/01/kwinx11-is-fe...
Yes, openSUSE, you should try that.
openSUSE has a massive test suite, called openQA, with which they automatically test their builds. And among other things, they also maintain two builds with the latest KDE commits on top of their more stable version openSUSE Leap and one on top of their rolling release openSUSE Tumbleweed (those builds are called Argon and Krypton respectively).
So, they have integration testing all the way through, prior to an official KDE release already.
This also means that they can essentially always ship the latest KDE Plasma LTS on openSUSE Leap without any problems.
And, KDE gives back for all of that effort and then schedules LTS releases to be relatively close to openSUSE Leap releases.
So, openSUSE is that distro that you're looking for, which takes this amazing desktop environment and makes a stable system out of it. Like, honestly it's hard to remember the last crash that I had (when I was not dicking around with random KWin scripts, that is).
The aforementioned Manjaro, I've also heard good things of, in that it at least does not treat KDE as a second-class citizen, but it's still miles away from all that extra effort that openSUSE puts in.
Definitely a thing to remember... Never mark a revision of successful software final when it's just alpha... ;)