When comparing JWM vs flwm, the Slant community recommends JWM for most people. In the question“What are the best window managers for Linux?” JWM is ranked 19th while flwm is ranked 25th. The most important reason people chose JWM is:
Jwm is a lightweight window manager that is used as the default window manager in Puppy Linux, a lightweight distribution that can be loaded from RAM.
Question Ranking
Pros
Pro Extremely lightweight
Jwm is a lightweight window manager that is used as the default window manager in Puppy Linux, a lightweight distribution that can be loaded from RAM.
Pro Great for older machines
Jwm is very easy on your GPU, making it very suitable for older machines that can't run other options quite as well.
Pro Menus load extremly quickly even on old hardware
Pro Reasonably easy to customize
No need to know a programming language.
Pro You can use windows not in the top stack
The user can click on a window and it will not raise, instead staying behind any other window. The user is then allowed to use the window, such as a terminal. It will remain below any other window until the title-bar is clicked.
Pro Straight-forward
Flwm doesn't come with as many features or extras as other WMs. This makes it a lot easier to set up and understand.
Pro Small & fast
Flwm is a small, speedy footprint window manager that does not use up a lot of resources.
Pro Window title bars maximize useable space
All windows title bars are placed sideways in order to maximize screen space.
Cons
Con Unattractive default theme
The default theme for jwm is not very visually appealing (though there are many themes available for users to change it as they please).
Con Lack of theme support
Flwm does not have any themes, so what you see is what you get - which is in fact rather dated looking.