I would recommend KDE Neon, it's been stable since years and rock solid. It's based on latest Ubuntu LTS but with the Plasma desktop that looks like Windows 10. And when you first install it, it's pretty empty (you just have the bare minimum apps: Firefox, Okular, VLC, …) From there you can choose what programs you want to install (Discover Software Centre) You get all the KDE apps up to date. It's a bit different from Kubuntu were you are always 6 months behind in terms of release.