KDE's terrible these days. I wouldn't use it unless you have a really good reason to - and I can't think of what that reason would be. I used it religiously for almost 25 years (from its creation in 1996, up until just a few years ago) but it's really gone to shit. Final straw for me was a pretty huge bug I had a ticket in for, it is/was acknowledged, but never fixed over the course of about a year. In the process of trying to get it sorted out / fixed, one of the (at the time) better-known KDE devs actually contacted me in private and said that nobody would ever fix that bug, because he was the only person remaining in the project who had the knowledge to fix it, and he was leaving the KDE project that very week, because he saw it as a dead/failed project.
I moved to Xfce, which I'd recommend. MATE and Cinnamon aren't bad either. GNOME 3 is an abomination.
That's bad news.
KDE was doing great except a confusion due to some redundancy left in the configuration panels (at least in openSUSE), but overall a solid choice. I haven't used it in a while, so it's sad to hear about that.
GNOME since version 3 isn't for everyone indeed, I don't mind a desktop environment that is a little more "complicated" to use but which lets me do what I want. It reminded me the Apple philosophy a little bit, and sure enough, the latest GNOME versions seem to look like macOS (I suppose one can configure that differently, at least). So I suppose my gripe is subjective and mostly with the window manager.
From my little experience, if you don't want to start digging into the configuration files, the safest way is to use one of the default desktops offered by the distribution. It's been tested by more people, and there's more doc and support.
On the other way, digging into the OS files is what Linux is all about, and that's the best way to learn it, even if it's daunting sometimes.
For example I've used Manjaro lately, which is great except the package management, but the Arch User Repository is nice to have. It comes with Xfce (that I'd recommend), KDE or GNOME. Community Editions come with Cinnamon, MATE and other things - like Deepin for anyone who'd dare touching that.
Mint is a very user-friendly distribution last time I checked. It offers by default Cinnamon, MATE and Xfce, all great choices. If I had to be Ubuntu-related, I'd choose one of those.
To be honest, the choice of DE becomes less and less important to me in comparison to the package management, the available repositories and the general state of the distribution.
That remembers me when I went to Sweden to work for a client and had to type on a weird keyboard for a few days. I loved the country by the way, beautiful and so peaceful!