When comparing Pantheon vs i3, the Slant community recommends i3 for most people. In the question“What are the best window managers for Linux?” i3 is ranked 1st while Pantheon is ranked 23rd. 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/).
Specs
Question Ranking
Pros
Pro Simple, clean aesthetic
Nonintrusive and easy to overview workspace.
Pro Smooth, subtle animations
Nearly everything is animated, but it's not over the top.
Pro Lightweight
Pantheon is light on system resources, giving it the advantage of being able run well on a multitude of setups.
Pro Splitting and animations
Switching between workspaces is fluid, pulling up the workspace preview bumps up the rest of the desktop, open windows show up on the switcher along with larger icons, and everything is subtly animated. You have two windows taking each half the screen by dragging to corners.
Pro Looks amazing
Looks absolutely amazing. Very nice to use. Amazing UX.
Pro Highly modular
While built to be integrated, Pantheon is also highly modular. Shell components like the Panel, Dock, and app launcher can be swapped out with limited repercussions.
Pro Great for minimalists
Although you cannot put icons on desktop, it comes with very low number of pre-installed softwares.
Pro Perfect for chromebook
It's light and easy.
Pro Slick, smooth desktop environment
Easy to use and easy to configure, there is almost nothing that the developers did not think of to creat a top-notch user experience.
Pro Excellent documentation
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, because they concern tools outside of i3 for example, there is the community question & answer site.
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 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 Fast, especially on weaker hardware
Tiling means there are no fancy compositing or window effects to take up system resources.
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 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 Terminal bell can be used to notify of completed actions
Terminal-bell gets passed through and marks the workspace visibly.
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.
Cons
Con Few configuration options
It is pretty bare-bones on a stock install, but further configuration options can be added through various official tweak tools.
Con Too simple
Good for people who want a plug and play simple Desktop Environment. But for a multitasking / entertainment / cutting edge or Gaming Rig this is not the answer.
Con Not ideal for enterprise environments
As it has no set release date, and no set support and/or EOL dates, that makes it a not so good choice for enterprises managing a number of machines where such dates are important to know before hand.
Con Slow maintenance
Any significant updates come with new release, which usually takes 2-3 years. Hence gets obsolete with current software.
Con Buggy
Con Not available for major Linux distributions
Con No icons on desktop
Con Uses GTK
Nowadays, GTK is designed with GNOME, and only GNOME, in mind. Non-GNOME applications which attempt to utilize it suffer as a result. Pantheon is no exception.
Con Looks and feels like a Mac
Which may turn quite a few people off with the aesthetics, of course for some people, this is a pro.
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 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 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.