When comparing SizeUp vs SMBAct, the Slant community recommends SizeUp for most people. In the question“What is the best window manager for Mac?” SizeUp is ranked 12th while SMBAct is ranked 32nd. The most important reason people chose SizeUp is:
SizeUp has user-configurable keyboard shortcuts for a set of pre-defined actions.
Specs
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Pros

Pro Keyboard centric
SizeUp has user-configurable keyboard shortcuts for a set of pre-defined actions.
Pro Supports multiple monitors / spaces
Windows can be sent to different monitors and spaces. It can also be aligned as needed.

Pro Simple
SizeUp is easy and simple to use without having to configure.
Pro AppleScript support allows extending functionality
AppleScript permits adding features such as tiling all open windows. Additionally, FastScripts it allows the user to add keyboard shortcuts to AppleScripts.
Pro Menubar dropdown for shortcuts
Learning a bunch of keyboard shortcuts right off the bat may be difficult to remember at first, which is why a menubar shortcut for the app exists with all the shortcuts listed.
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 Nag window
If a license is not purchased there is a nag window (which suspends function) that pops up when loading the app (at user login). The nag pop-up is also summoned at certain time intervals and by performing a certain number of commands (manually or by keyboard shortcut).
Con No on-the-fly split screen window settings
Unlike some other tiling window managers, SizeUp has no way to change the size of split screen actions on-the-fly. Any time a user wants to change how much room on the screen a window takes up when using the split screen function, they will need to manually change the settings, which can be time consuming.
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.
