When comparing Ungit vs Intellij IDEA, the Slant community recommends Ungit for most people. In the question“What are the best Git clients for Windows?” Ungit is ranked 21st while Intellij IDEA is ranked 23rd. The most important reason people chose Ungit is:
Ungit is open source software available under the MIT Licence.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Free and Open Source Software
Ungit is open source software available under the MIT Licence.

Pro Cross-platform
Works on Windows, Linux, and OS X.
Pro Optional Integration with Modern Text Editors
Ungit can be integrated directly into modern text editors, Atom, Brackets, and VS Code.
Pro Web-based interface
Ungit is web-based, meaning you can run it on your cloud/pure shell machine and then use the UI from your browser.
Pro Free version available
There is a free community edition (open source) and an ultimate edition, which you can compare here.
The ultimate edition is available for free for one year for students but must be registered through an .edu e-mail account.
Pro Fast and smart contextual assistance
Uses a fast indexing technique to provide contextual hints (auto-completion, available object members, import suggestions).
On-the-fly code analysis to detect errors and propose refactorization.
Pro Intuitive and slick UI
IDEA has a clean, intuitive interface with some customization available (such as the Darcula theme).
Pro Stable and robust
IntelliJ IDEA hardly ever crashes or has any issues that plague other Java IDEs like file corruption or slowness.
Pro Support for many languages
IntelliJ supports many languages besides Java, some of these are: golang, Scala, Clojure, Groovy, Bash, etc...
Pro Smart refactorings
IDEA places an emphasis in safe refactoring, offering a variety of features to make this possible for a variety of languages.
These features include safe delete, type migration and replacing method code duplicates.
Pro Lots of plugins
Many plugins are available for almost any task a developer may need to cover. Plugins are developed by Jetbrains themselves or by 3rd parties through the SDK available for writing them.
Pro Android support, JavaEE support, etc
A very complete development environment support.
Pro Clear and detailed documentation
The documentation is exhaustive, easy to navigate, and clearly worded.
Pro Very powerful debugger
With ability to step into a certain part of a large method invocation (Shift+F7), drop frame, executing code snippets, showing method return values, etc.
Pro Many convenient features
These simplify the daily work, e.g. copy/cut a whole line without the need to select it.
Cons
Con Node.js dependent

Con Setup is not user-friendly
Ungit is distributed as an NPM package and requires git and Node.js to be installed on your system before you can run it. Ungit must be launched by running ungit
in a command line terminal.
Con Exposes git commands to your network
No authentication, if someone can communicate with your computer on the port this is running on, they can execute any git command they want on your repos as well as view your filesystem's folders.
Con Bugs are not solved as often as they should
They are more interested in adding new features or issuing new versions than solving bugs.
Con Somewhat expensive
IntelliJ IDEA is fairly expensive, with a pricetag of $149/year.
However there is a free community edition available.
Con Built with closed source components
The version with full features is not opensource. Parts of the code are under apache licence though.
Con Lack of plugins
IntelliJ supports a very small amount of plugins. Althrough thesse are 'quality approved', many features are missing and can't be implemented because of that.
Con Standard hotkeys behave differently
Seems like hotkeys assignment in Idea has no logical consistency.
Like «F3» is usually next match, «Ctrl+W» - close tab, etc — they map to some different action by default.
There is a good effort in making the IDE friendly for immigrants from other products: there are options to use hotkeys from Eclipse, and even emacs. But these mappings are very incomplete. And help pages do not take this remapping into account, rather mentioning the standard hotkeys.
So, people coming from other IDEs/editors are doomed to using mouse and context menus (which are rather big and complex).
