When comparing Slate vs Spectacle, the Slant community recommends Slate for most people. In the question“What are the best power user tools for macOS?” Slate is ranked 21st while Spectacle is ranked 37th. The most important reason people chose Slate is:
Ranked in these QuestionsQuestion Ranking
Pro Extremely configurable
Pro Lets you set default layouts
By using a feature called "snapshots", users can set up different default window layouts in Slate that they can switch to and from on the fly.
Pro It's free
Slate is completely free to download and use, which is a great option in a field of Mac WMs that often costs money to use.
Pro Based on hotkeys
Hotkeys can be set to re-size and focus windows, as well as activate layout presets.
Pro Window hints
Slate offers window hints which are an intuitive way to change window focus.
Pro Allows for tiling
Slate allows for customizing the config file in order to emulate tiling windows.
Pro Free and open source
Spectacle is licensed under MIT with source code available on GitHub.
Pro Simple hotkeys
Spectacle offers easy-to-remember preset hotkeys.
All windows in Spectacle can be controlled with keyboard shortcuts, so no mouse is needed. This makes for a fast way to control windows.
Pro Low footprint
Spectacle only uses up 18-19 MB of RAM, which means there is not much overhead by using this app.
Pro Great UX
Spectacle is easy to use and configure. It's plug and play.
Pro Multi-monitor support
Con Project maintainance is on pause
The developer is currently taking a pause to focus on other things as of December 2015.
Con Hard to configure
There's no graphical user interface for configuring Slate, meaning it has to be done from the command line interface or by editing a config file. This makes it somewhat difficult and time-consuming.
Con Missing features
Unable to perform all tasks of software it was meant to replace.
Can not move windows between 'Spaces' (virtual desktops).
Con Video fail
Demonstration video failed to highlight any of the advantages of the windowing system. Or at least, the advantages were so subtly intrinsic that no-one who didn't already use the system could appreciate them.
Con Breaks on macOS High Sierra / Chrome or Firefox
Doesn't support side by side windows.
Con Impossible to add new functions
While keyboard shortcuts can be changed for the available actions, there is no way to add custom actions which in turn limits the functionality of the app.
Con Limited window sizing capabilities
You can use 1/2 of the screen vertically and horizontally (divide into 4 parts). You can also use the screen in thirds too, but only the left and right third: you can't use the 1/3 in the center. There is no way to do a more granular distribution.
Con Not maintained
The software is free, but no longer seems to be maintained.
Con Doesn't work with any Adobe products
There are some apps like Adobe Reader that do not work with Spectacle. Basically, any app with a heavily customized UI that breaks OS X accessibility will not work correctly under Spectacle.