When comparing Parallels Desktop vs TotalTerminal, 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 Parallels Desktop is ranked 59th. 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 Best-in-class gaming performance
Compared to other VMs, Parallels has the best gaming performance. Still, a good framerate can only be achieved with games that have very low resource requirements. A much better option for resource intensive games is dual booting Windows (via Boot Camp).
Pro Easy to use
Parallels has an easy to learn and use UI. All important features are wizard based. It requires only a few clicks for the wizard to download and set up the latest Chrome OS, Windows or Linux build.
Pro Can run Windows apps as native OS X apps
Parallels has a "Coherence View" mode that allows running Windows applications as if they were native OS X apps. In this mode Windows is virtualized in background and Windows features like Jump Lists, Taskbar, Start Menu, etc can be embedded directly within OS X.
Pro Best integration ever
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).
Cons
Con Very expensive
Parallels upgrades are very expensive. Even if I bough several versions of Parallels I will switch back to free VirtualBox as they even "invented" the Pro version - mainly doubled the price you have to pay each year to have the software updated.
Con Can't import OVA files
OVA files are useful because they include all of its supporting files. Unfortunately, Parallels doesn't support these useful files.
Con Requires buying a new version of the software with each new OS X release
Chances are that the same version of Parallels won't work with different OS X releases, requiring a separate purchase of Parallels for each OS X version.
Con Home edition doesn't work with Vagrant or Docker Machine
Make sure you purchase the Pro edition (the subscription) if you need command-line access to the hypervisor.
Con Can't export OVA files
One you use parallel you get trapped into a proprietary format.
Can't share disk blocks on two unrelated virtual machines (KSM for disk) too.
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.