When comparing Amethyst vs SMBAct, the Slant community recommends Amethyst for most people. In the question“What is the best window manager for Mac?” Amethyst is ranked 5th while SMBAct is ranked 32nd. The most important reason people chose Amethyst is:
Amethyst is published under the MIT license making it open-source and id offered completely free. This allows anyone to give the tiling window manger a try, which is great.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro It's free and open-source
Amethyst is published under the MIT license making it open-source and id offered completely free. This allows anyone to give the tiling window manger a try, which is great.

Pro Recently updated and rewritten in Swift.
The application was written in Objective-C, but was recently updated and completely rewritten in Apple's new native language Swift.

Pro Works with keyboard shortcuts, no mouse needed
As it's designed to work closely to how xmonad, Amethyst uses keyboard shortcuts to control the windows being used, meaning no mouse input is necessary. This can make for a faster way to control windows.
Pro Multi-monitor suppport
Pro Has many common layouts to choose from (fullscreen, floating, row, column, wide, etc)
Pro Can switch between tiling and floating mode
Pro Under active development
Pro Configured via UI
No CONFIG file provides security and will avoid making amethyst crash. Instead configured via simple UI
Pro True tiling means never losing track of windows under a huge pile of others
Pro Window manager + switcher
SMBAct works not only as a tiling window manager, but also as a window switcher. This ensures smooth transitions from one functionality to another when you work with two monitors.
Pro Good for those who prefer the keyboard to the mouse
You can do everything with the keyboard. Many preset hotkeys for different actions, but you can set your own. Easy to find and activate any action even if you forget the hotkey through a special window with a quick search.
Pro User friendly
There is a video tutorial with detailed descriptions of how to use it. In addition, the program itself has a lot of tips.
Cons
Con Can be buggy at times
Con There are more user friendly window managers available
There are certainly more user friendly window managers available for MacOS, such as Divvy or Moom. Amethyst, however, is more powerful and customizable than the more user friendly options available and therefore may be a better choice for a user looking for more advanced capabilities and customization.
Con Not free
Can be used for free for a month right now, but it's generally available for a fee after free-trial: $14.00.
Con No possibility to snap to the edges and corners
They promise to add it in the next update, but it is currently not present.
