When comparing SizeUp vs Swish, the Slant community recommends Swish for most people. In the question“What is the best window manager for Mac?” Swish is ranked 8th while SizeUp is ranked 12th. The most important reason people chose Swish is:
Gestures are faster than dragging or keyboard shortcuts.
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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 Best window manager for trackpad power users
Gestures are faster than dragging or keyboard shortcuts.
Pro Multi-monitor and spaces support
Switch intuitively between screens and spaces based on their physical location.
Pro Sleek and intuitive
Pro Easy to use
Intuitive gestures, doesn't get in the way like BetterTouchTool.
Pro Custom grid offsets
The default setting uses a clean single-pixel divider without any overlaps.
Pro Matches the Mac language
Pro Fast
Just squeezing on top of an icon to close the app is a breeze compared to right clicking and selecting "quit," using Command + Q, or APP NAME -> Quit.
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 The tutorial within the app is not that thorough
Con Limited keybinding customization
