When comparing i3 vs KWin, the Slant community recommends i3 for most people. In the question“What are the best window managers for Linux?” i3 is ranked 1st while KWin is ranked 8th. The most important reason people chose i3 is:
Every feature is thoroughly documented (including examples), and documentation is kept up-to-date. For questions that are not answered by the i3 [user guide](http://i3wm.org/docs/userguide.html), because they concern tools outside of i3 for example, there is the community [question & answer site](https://faq.i3wm.org/).
Ranked in these QuestionsQuestion Ranking
Pro Fully configurable (including tiling)
One of the biggest attractions of i3 is that it can be configured just about any way the user likes. Ranging from custom keyboard shortcuts to placement of opened apps, it is up to the user as to how they would like their window manager to behave.
Pro Easily readable plain-text configuration
i3 has plain-text configuration, meaning that no lua or haskell is needed. This makes it rather easy to recommend i3 to other people without worrying whether or not they have the knowledge to configure it as it can be read by anyone without prior knowledge.
Pro Easily switch to and manage floating windows
i3 can allow for the user to manage floating windows. Floating mode can be toggled by pressing $mod+Shift+Space. This way the user can take advantage of tiling as well as floating windows, all in the same session.
Pro Can tab windows
i3 permits tabbing through windows by turning on tab mode with $mod+w.
Pro Fast, especially on weaker hardware
Tiling means there are no fancy compositing or window effects to take up system resources.
Pro RandR support
RandR provides more information about your outputs and connected screens than Xinerama does. To be specific, the code which handled on-the-fly screen reconfiguration (meaning without restarting the X server) was a very messy heuristic approach and most of the time did not work correctly — that is just not possible with the limited information that Xinerama offers (just a list of screen resolutions and no identifiers for the screens or any additional information). Xinerama simply was not designed for dynamic configuration.
Pro Can stack
i3 allows for stacking of windows in its environment.
Pro Can be reloaded quickly and configured without a client restart
Just two hot keys: Shift+Super+C to reload the config and Shift+Super+R to restart (which takes less than one second). Restarts pick up new versions of i3 or the updated config file, so you can upgrade to a newer version or quickly see the changes to i3 without quitting your X session.
Pro No window gap
Space is not wasted by separators, therefore making the most of the confined space on smaller monitors.
Pro Terminal bell can be used to notify of completed actions
Terminal-bell gets passed through and marks the workspace visibly.
Pro Sane development process
i3 uses test driven development with an extensive test suite to prevent bugs from ever happening again. All external contributions require a thorough code review to guarantee a certain level of quality.
Pro VIM Style key bindings
You can configure i3 so that your keys for moving windows is similar to vim, for example, M-j to move the window down.
Pro Simple to use
Configuration is nearly automatic and simple, which can be really helpful to beginners.
Pro Awesome multi-monitor support
User can assign specific workspaces to specific displays as well as apps to workspaces. This makes possible opening set of most used apps with 1 shortcut always on the same screens.
Pro Never have to take hands off keyboard
Keyboard shortcut based navigation can seem daunting at first, but one quickly gets used to it. It enables the user to never have to take their hands off the keyboard, meaning that they can use their computer quickly and efficiently.
Pro Layouts can be saved and reused
Pro Great choice for keyboard users
The user keeps their hands in one spot (most of the time). One will find that the mouse is used less and less, making navigation quicker over time.
Pro Highly configurable
KWin has a very configurable environment. Just about any option that you would like to adjust will be available in the settings.
Pro Integrated compositing manager
KWin has built-in compositing with options on how it performs that can be changed by the user in the settings.
Pro Offers desktop workflow
In an age where everyone seems to be moving to touch interfaces, KDE remains one of the last DEs that still caters for desktop users.
Pro Beautiful interface
KWin has an assortment of attractive desktop effects, creating a rather beautiful interface.
Pro Window effects
KWin offers an assortment of window effects, such as wobbly windows and window shadows/glow.
Pro Effortless VSync
VSyncing with NVIDIA blobs can be tricky (the dreaded tearing) but with KWin, video and OpenGL games display flawlessly.
Con Missing "include" possibility in config
While pretty good and easy to use for common tasks, the configuration language is missing the
include directive common in other languages. You can use a workaround - a shell script to config parts on demand. It would be best if this were built-in however.
Con No window gap option
You can do a lot with i3 but the official version lacks the option to have gaps between windows. However, there's a fork called i3-gaps that is almost the same as i3 except the fact that it lets you have gaps between windows.
Con Poor floating window support
Sometimes this is necessary, even when the Dev rejects feature requests. Firefox child windows (option dialog) is an example.
Con Steep learning curve
Has a steep learning curve for beginners.
Con Not very configurable
Unlike XMonad or Awesome, i3 can't be configured in a turing complete language, so it is much harder to alter its core functionality to do exactly what the user wants.
Con It has some issues with transparency
Using transparent windows can cause them to crash.
Con The plain-text configuration may not be suitable for beginners
i3 is configured through a plaintext configuration file. While it's very powerful and easy to learn, it may not be entirely user-friendly for those who have never edited a text configuration.
Con No shortcut to switch between two recently used applications/windows
You can easily switch between two workspaces but not two windows (which are not adjacent to each other). The functionality simply isn't there and the dev refuses to include it as a part of i3 core. This can get annoying when you have multiple windows in the same workspace. There is a manual workaround though.
Con Manual tiling
The layout isn't automatic. The user must move panels manually and may indeed end up spending time on that rather than on working with the application.
Con Documentation is online
Can't access it offline unless you download the page.
Con Dependent on some KDE libraries
This makes stand-alone KWin somewhat inconvenient to set up, as opposed to openbox and awesome, to name but a few.
Con Some effects are slow and jerky
Some of KWins effects (such as present windows) can be a bit slow or jerky, resulting in uneven fluidity. This is no longer true on modern versions.