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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
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Security
When you use X11, you allow any program running on your computer to access anything on your screen and clipboard, collect your keystrokes and type. It's trivial to implement a keylogger, for example. Do not buy into the whole "no viruses on Linux" thing, it's not true and likely to become even less and less true, as desktop Linux is becoming popular.
Wayland at least tries to put some barriers in place against this.
I don't think for tue average user it really matters much. If you've got multiple screens of different sizes or refresh rates, Wayland is the way to go. If you've got multiple identical screens that you want to treat as a single big screen, X11 is perfect for that.
I recently switched and I'm happy with how it runs. Even on Nvidia.
X11 is dead don't bother with it. The same people who wrote X11 are working on Wayland because X11 became to here maintain.
X11 has many features and some it will never have. Wayland has less features and it has compatibility issues for the ones it has. But if you need 4K or touchscreen then Wayland is the way to go. Default choice should probably be Wayland unless it doesn't support that one thing you care about.
X11 is still server-first and needs workarounds to run locally (like startx, sx), while Wayland can just be run. Unlike X, it isolates every processes access to other windows, but with slow adoption of protocols for things like screen-sharing, video conferences, accessibility tools. The tooling is not yet there imo.
That's the main difference nowadays. Some people have issues with tearing or wrong-monitor with either of them.
Honestly, Wayland vs. X (and Flatpak) fit this perfectly: 
If you use a feature complete Wayland compositor and compare it to equivalents (RIP velox), then Wayland basically offers more consistent pen and multitouch support and stuff, while being faster.
There's no 2D acceleration in Wayland and that's by design, it's made for new GPUs that don't have 2D anyway anymore. Programs either draw pixels or start up 3D.
XLibre is trying the opposite and is actually merging various 2D drivers for old and niche hardware, like ct65550 as found in the Toshiba Libretto 50ct among others. Most of these originate from distribution forks (NetBSD in this case). T2 Linux also maintains a patch to bring back lots of more ancient 2D drivers that were removed in 2012.
Every time I setup my desktop up for Wayland I always go back to X11, I find Wayland sluggish compared to X11 and don’t have the time nor energy to troubleshoot applications that had no issues working on X11.
I did not have any problems with Wayland for 6 months on Arch (personal PC for hobby projects and gaming). I also don't want to troubleshoot, it just works. Most applications are installed via flatpak.
also don't want to troubleshoot, it just works. Most applications are installed via flatpak.
I’m not surprised Flatpaks work with Wayland without issue, however Flatpaks containerize the application which is something I don’t want to do for everything I download as it adds extra overhead for something that could’ve just been built and installed as a native package (.deb, .rpm).
To each their own though.
Yes. This is still an important point, you make!
Wayland has been the default for awhile, but open source software is maintained by volunteers.
Until each specific package has been updated by the original developers, it may not work well on Wayland.
So, for now, there's also a trade-off:
As some general advice: If you don't know the specifics, just go with your Linux distribution's defaults. They probably have this figured out for you. Wayland is the more modern approach. We had a long transitioning period and some things didn't work for a while or were missing. I'd say it's ready by now. And if your distro maintainers also think it's time to supersede the old X server, it probably is.
Some things still don't work on Wayland.
(Like screen sharing with Anydesk, as an example I ran into yesterday)
But at this point, I just replace the thing that still requires X11 with an alternative, or find a different solution.
X11 is dead tech. Wayland has its own issues, but it's better than X11 in almost every way now, actively maintained, and it's the current standard.
Wayland is more secure than x11 by design and more concise in scope. Notably it supports contemporary display technologies like display independent scaling, VRR, colour space (HDR) and several others.
Wayland is made by the x11 people.
one thing i noticed in trying both is x11 using more cpu in the same scenario (playing a youtube video, same resolution) and even the DP adapter i am using getting warmer when on x11 compared to wayland. in this scenario the difference wasn't much despite being roughly double (~2.5W compared to ~4.5W in x11). idk how that scales in other scenarios.
By real user, do you mean a nontechnical user? If that's the case, the display server isn't a choice to be made by such user, but by the distro maintainers. Most people won't notice the difference, because it's mostly stuff that happens under the hood.
I mean the ELI5 for the uninitiated is that X11 is older, and Wayland was made as the successor to X11. It aims to address issues that a lot of people had with X11. X11 is not in active development whereas Wayland is, and for support for modern tech, it'll be added to Wayland but not X11. These days I'd advise to go with Wayland unless you either have hardware that doesn't place nicely with it or you have a specific use-case for X11, i.e. Wayland unless you have a reason not to. Although most "beginner" distros choose for you without prompting you to pick, in which case go with the default (it's probably Wayland anyway).
If you mean to explain the debate, basically some people have particular things they want to do, or they want to do something a certain way, and it's not supported by Wayland, usually by design due to things like security concerns or philosophical differences with X11. X11 will continue to work for a long time but it's not getting new features, so if these issues are a concern with you, you could stick to X11 for the foreseeable future.
The average user is not supposed to notice a difference (apart from maybe QoL differences like performance, screen tearing, etc)—that's the goal of both projects. It should just display your desktop.
X11 is stable and maintained but not getting new features. It will generally work well for most people but over time it will and is drifting to obsolesence.
Wayland has some flaws but is not basically stable and feature rich enough for most people to use. It is not a complete drop in for X11 and won't necessairly ever will be but for the vast majorory of desktop users it is.
The problem with Wayland is that there are still issues for people with graphics drivers. Nvidia in particular has had serious issues with it although they are improving.
I personally still use X11 with my KDE set up because i still have problems woth Wayland. Thwyre not as bad as they were but its still not quite stable above for me.
Is it even a debate at this point? x11 is on it's way out and wayland transition is pretty much complete within the gnu/linux ecosystem. Vast majority of distros and desktop environments ship with wayland as the default and keep developing with wayland in mind, with holdouts like debian and mint that still use x11, I think. X11 is basically dinosaur software for legacy. Vast majority of end users will just take what is the default and that is Wayland and they don't even notice.
On most distros Wayland is trouble free and x11 is a thing of the past. X11 made some things simpler like screen share with somebody , but Linux is growing large enough that Wayland (that is secure) is the best choice. You don't want your x11 screen duplicated on a malware attackers screen etc.