When comparing TotalTerminal vs SizeUp, the Slant community recommends TotalTerminal for most people. In the question“What are the best power user tools for macOS?” TotalTerminal is ranked 20th while SizeUp is ranked 57th. The most important reason people chose TotalTerminal is:
TotalTerminal is a plugin for Terminal.app. It provides persistent Visor Window which slides down when you press a hot-key.
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Pros
Pro Allows quick access to the terminal system-wide
TotalTerminal is a plugin for Terminal.app. It provides persistent Visor Window which slides down when you press a hot-key.
Pro Quake style window show/hide
You maybe know or don't know Quake from Id Software. But this game had the best idea to hide/show a terminal window. Simply using full width but 26 rows. On show the widow slid down from top of screen. On hide it mode up to top edge of the screen until it disappeared. 2nd next best was the semi translucent background. You could still see through the terminal window while it was shown.
The same style is now available in TotalTerminal and iTerm2 (OSX Terminal replacement - no Terminal plugin).

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.
Cons
Con No longer under active development
Con Doesn't work on El Capitan with SIP on
Apple introduced a new security feature in OSX El Capitan, called System Integrity Protection, that, among other things, does not allow augmenting Terminal. While it's possible to turn SIP off (instructions on how to turn off SIP and get TotalTerminal working on El Capitan can be found here) it is not recommended.
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.
