When comparing Emacs vs Intellij IDEA, the Slant community recommends Intellij IDEA for most people. In the question“What are the best IDEs for web development?” Intellij IDEA is ranked 9th while Emacs is ranked 11th. The most important reason people chose Intellij IDEA is:
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.
Ranked in these QuestionsQuestion Ranking
Pro Keyboard-focused, mouse-free editing
Emacs can be controlled entirely with the keyboard.
Pro Total customizability
Customizations can be made to a wide range of Emacs' functions through a Lisp dialect (Emacs Lisp). A robust list of existing Lisp extensions include the practical (git integration, syntax highlighting, etc) to the utilitarian (calculators, calendars) to the sublime (chess, Eliza).
Pro It's also an IDE
You can debug, compile, manage files, integrate with version control systems, etc. All through the various plugins that can be installed.
Pro Works in terminal or as a GUI application
You can use Emacs' command line interface or graphical user interface.
Pro Self documenting
Emacs has extensive help support built-in as well as a tutorial accessed with C-h t.
Licensed under GNU GPL.
Pro Great documentation
With 30+ years of use the Emacs documentation is very thorough. There are also a lot of tutorials and guides written by third parties.
Pro Mini buffer
You can pass complicated arguments in the mini buffer.
Fully compliant GNU-emacs is available on many platforms, and they all understand .emacs configuration files.
Pro Rectangular cut and paste
Emacs can select rectangularly.
Pro Lisp customizations
With lisp customization, any behavior of Emacs can be changed. Update with pre-release patch can be also applied without recompiling the whole Emacs.
Pro Vi keybindings through Evil mode
Evil mode emulates vim behaviors within Emacs. It enables Vi users to move inside the Emacs universe.
Pro Visual selection and text objects with Evil
Evil is an extensible vi layer for Emacs. It provides Vim features like Visual selection and text objects.
Pro Support multi-line editing, multiple frame, powerful paren, crazy jumping style
Review the "Emacs Rocks" video.
Pro Provides org-mode
Advanced planning and publication which can start as a simple list.
Pro Has been widely used for a long time
Pro dabbrev-expand (Alt-/)
Dynamic word completion.
Works on Linux, Windows, Macintosh, BSD, and others.
Pro Enormous range of functionalities (way beyond simple "text editing")
Through its programmability, a very broad range of functionalities can be integrated in emacs, turning it even into a "single point of contact" with the underlying operating system.
Pro Integrates planning in your development process
You can jump straight from your org-mode files to programming tasks - and back - and build a seamless workflow.
Pro Helm plugin adds even more power to Emacs
Powerful commands, search, and more with the Helm plugin.
Pro GTK+ widgets support
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 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 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.
Con Learning curve is long
While it's better than it used to be, with most functions being possible through the menu, Emacs is still quite a bit different from your standard editor. You'll need to learn new keyboard shortcuts.
Con Sometimes the extensibility can distract you from your actual work
If I ever want to lose half a day, I'll start by tweaking my .spacemacs config file.
Con Chorded keyboard combinations can be baffling
For example, for navigation it uses the b, n, p, l keys. Which for some people may seem strange. But don't worry, you can change it.
Con A lot of jokes in this serious software
Con Using Emacs on a new machine without your .emacs file
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 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 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).