When comparing XMonad vs WMFS2, the Slant community recommends XMonad for most people. In the question“What are the best window managers for Linux?” XMonad is ranked 3rd while WMFS2 is ranked 28th. The most important reason people chose XMonad is:
XMonad is written, configured, and fully extensible in Haskell. This means that users aren't limited to a small set of pre-programmed layouts and actions: anything can be programmed into the configuration. It's simple to modify basic settings, and the example config has lots of comments to get you started. Haskell keeps this code clean, concise, and readable, and its type system keeps you safe from any serious mistakes. This makes it fast and light, even on very small and slow systems.
Question Ranking
Pros
Pro Fully extensible with Haskell
XMonad is written, configured, and fully extensible in Haskell. This means that users aren't limited to a small set of pre-programmed layouts and actions: anything can be programmed into the configuration.
It's simple to modify basic settings, and the example config has lots of comments to get you started. Haskell keeps this code clean, concise, and readable, and its type system keeps you safe from any serious mistakes. This makes it fast and light, even on very small and slow systems.
Pro Efficient to use
XMonad is a very minimal and efficient window manager, especially if the user is familiar with Haskell.
Pro Absolutely minimal
The entire window manager is extremely small, and includes nothing beyond basic window manipulation and tiling. Out of the box, there are no window decorations, status bar nor icon dock; just clean lines and efficiency.
Pro Very stable
Use of Haskell, in conjunction with smart programming practices, guarantees a crash-free experience.
Pro Edit configuration and reload on-the-fly
Configuration is compiled into the WM, and it can be changed/updated on-the-fly, without requiring a full reload.
Pro Great availability of libraries
The use of Haskell as an extension language means that popular pieces of functionality are easily shared and widely available as Haskell Libraries. Many default layouts, and tools for quickly and easily building your own, are available through XMonad-contrib, and highly re-usable configurations are commonly shared through blog articles and the Xmonad Wiki.
Pro Highly configurable
If you enjoy programming, you can even add features to XMonad to make it your perfect desktop environment, and the Contrib modules give you most of what you need to do exactly that.
Pro Handles multiple monitors well
XMonad can handle multi-monitor setups by default.
Pro Xinerama support
XMonad has full support for Xinerama: windows can be tiled and managed across multiple physical screens.
Pro Dynamic Tiling
XMonad uses dynamic tiling which means that it automatically handles arranging your windows into various layouts which the user can cycle through.
Pro Built-in panel
WMFS2 has a status bar built into the desktop. This implies that no extra app is required for users who like to use a panel on their desktop.
Pro Multiple desktops
WMFS2 utilizes a feature called "tags" which is very similar to virtual desktops. With tags, WMFS2 can display multiple desktops in a singular desktop, as well as separate ones also.
Pro Easy to customize
WMFS2 uses a singular configuration file that is easy to edit and understand.
Pro Good mouse support
Re-sizing and moving tiled windows with the mouse is easy and intuitive.
Pro Supports tabbed view
WMFS2 has tabs like i3 WM. The bottom tile has three tabs, with only one visible window. Press alt+shift+k (by default) to get a combined tabbed window.
Cons
Con Steep learning curve for uninitiated users
Like a lot of tiling window managers, the learning curve for XMonad is quite steep.
Con Requires knowledge of Haskell for configuration
Understanding of Haskell is required in order to configure XMonad.
Con Requires a lot of Haskell dependencies
XMonad depends on GHC (the Glasgow Haskell Compiler) which can take up about 700 MB or disk space.
Con Bug with tag numbers on Debian
There is a bug where the tag numbers do not highlight correctly on Debian (though this may get fixed in the future and may not be a problem on other distros).