Linux

Yeah, this may not be helpful for you but the best GUI is a tiling window manager (compositor?). Using it for 2.5 years, never looked back. I really recommend Hyprland for everyone to try, it's the perfect thing we've ever needed.

I've been preferring KDE lately tbh. Very flexible and familiar. Still don't know what that activity thing is for though lol

I'm more of a window manager person myself (Qtile to be precise), and I imagine that's not really what you're looking for here, but DE-wise from what I've tried I like KDE and XFCE the most

I'm not aware of any distro that ships this by default yet, but Hyprland is my favorite visually so far. Excited for it to continue to develop. I'm sticking with Sway for now, Hyperland's grouping isn't nearly as extensive as Sway's tabbing and stacking, hopefully that will come eventually, but Hyprland sure does look amazing.

Fedora. It ships vanilla GNOME which is just a very pleasant experience. Vanilla GNOME is just something else man.

I think i3 looks really pretty

I've been using i3 for the past 8 years or so, and can wholeheartedly recommend it (or it's cousin Sway if you're in Wayland-land) if you're into tiling window managers (there are dozens of us!). I find them invaluable for their keyboard-centric operation, and also massively sweet on ultrawide monitors. Light on resources and minimalistic too.

As far as distributions go, I've been on Arch for the past several years. I think there are some (unofficial) spins for most Linux flavours with i3 out-of-the-box.

I used XFCE for a long long time before I went to tiles, which is a decent more traditional Window Manager, with a more lean focus than some of the others. Fairly customizable. I still use some of the system apps from there from old habit.

I wouldn't get too tied up into what window manager is default in any given distribution. At least for me, part of the joy is finding a combination of software (including the desktop environment/Window Manager) that works for you specifically. And there are plenty of live CDs (or usb images now I guess) with various WMs that can be used to take things out for a spin without commiting to installing it. :) Here are various Ubuntu flavors for instance.

Pop yea? Yeah?!

My vote would be EndeavourOS with KDE Plasma.

I liked zorin os

Kubuntu or KDE Neon 100%

Ultimately they both use the KDE Plasma desktop environment, which is the only DE I've ever seen that has a proper modern look by default (others IMO look like either the 2000's or an OS 4 Kidz), as well as being pretty featurful for multi monitor productivity

Arch+KDE Plasma is what I personally am gonna switch to this summer

Nitrux, it's a Debian distro with KDE, a rather classic pair indeed, but their Maui Kit is what makes it really stand out IMO... Well worth a look 😁

I really like the GUI in Pop!_OS. It's a custom GNOME installation with some sort of window tiling manager I don't know what it's called-- not sure what it's called, but I adore it. I really like it, and I like their system themes, too. It's very macOS-like. Simple, clean, and functional with a lot of little custom tweaks put in by system76 to cover some gaps in GNOME's basic configuration and things that are missing from Ubuntu (Pop!_OS is an Ubuntu variant).

Others have mentioned Linus Mint with Cinnamon. I haven't used it in several years, but I recall it being very nice and simple. It's very Windows-like, which I'm not a fan of, but the interface was quite pretty, as I recall.

All of them. Every distro can run any desktop, so all of them.

I haven't been on Linux for a while, but I tried out Ubuntu many years ago. I remember there was an update on GNOME that I really liked, before Ubuntu decided to replace it with its own UI? I'd have to dig into what happened because I completely forgot even the year when it happened.

Anyway, I remember liking that new GNOME look. Not sure if it has changed again or not.

I am into KDE Plasma, it works quite well on my distro (Fedora by the way) and one thing that I like about is is that I can make it truly mine. Defaults are nice, however sometimes I think I don't need that or need something else, and quite often I manage to do it to be the most comfortable for me. It's also very customisable and with enough learning you could rice it into quite a lot of stuff, even though I myself don't really know a lot how people do it.

I probably switch what I'm using every few months. The thing I cannot live without though is tiling support, whether just inherent to the window manager I'm using or an extension, I find it painful to use a computer for anything serious without one now.

Currently using KDE with the Bismuth extension (Fedora Kinoite) which isn't perfect but not bad. I'm eyeing Hyprland up from afar but as an Nvidia user I have too many issues on Wayland at the moment.

For me, it's Fedora + KDE when I need a GUI. I used to be an AwesomeWM guy for a very long time but I needed a proper GUI for my 5 year old. I'll convert her to i3 or Awesome one day....

I use KDE Plasma on RebornOS (an arch spin).

XFCE

I've been using linux on and off since my first experiments with zipslack back in 2000-2001, and full time since 2006. I've bounced around distros, tried countless DEs and WMs, and I have to say, Mint Cinnamon was the first where I didn't have to immediately change the theme/icons/color schemes/etc. to make it look decent (in my opinion). And add to that a more traditional desktop paradigm at a time when others (unity, gnome 3) were trying something else, and I was a convert, and still use it to this day, some 8+ years later.