When comparing rxvt-unicode vs Yakuake, the Slant community recommends rxvt-unicode for most people. In the question“What are the best terminal emulators for UNIX-like systems?” rxvt-unicode is ranked 1st while Yakuake is ranked 10th. The most important reason people chose rxvt-unicode is:
Rxvt-unicode uses very little memory and takes a lightweight approach without losing many important functionalities. A single instance of urxvt takes about 6.5MB-8MB of RAM.
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Pros
Pro Low memory usage
Rxvt-unicode uses very little memory and takes a lightweight approach without losing many important functionalities. A single instance of urxvt takes about 6.5MB-8MB of RAM.
Pro Can be daemonized to reduce resource usage
For those who want to lower their system's resource usage, rxvt-unicode allows for daemonization. This way you can run several instances of urxvt inside a single process.
Pro Supports terminal transparency
Changing the transparency of the terminal is allowed for in rxvt-unicode. This not only makes for eye candy but is also good for GUI usability.
Pro Minimum dependencies and simple text config
Pro Supports multiple font types
Multiple font types can be displayed flawlessly in rxvt-unicode.
Pro Handles bold text colour properly
Displays characters with text attribute bold actually as bold glyphs.
Pro High performance
Rxvt-unicode is much faster than most alternatives.
Pro Unicode support
International language support is provided through Unicode.
Pro Proper wrapping support
During selection and pasting wrapped text doesn't break into lines at place of wrapping.
Pro Fast text rendering
Rxvt-unicode has very fast text rendering, being able to render hundreds of MB of text in a very short time.
Pro Built-in Perl interpreter
It has a built-in Perl interpreter, meaning that no install is needed. Simply run urxvtperl
.
Pro Drop-down terminal makes for ease of use
Yakuake is a drop-down terminal. This means that you can press, for example, F12, and it slides downward from the top edge of the screen. After you are done with it, you can then hit F12 again and it slides back on top.
Pro Very customizable
Almost everything in Yakuake is customizable: from split view, fullscreen mode, configurable dimensions, to animation speed and keybindings.
Pro Split layout
You can easily split any tab into different windows and run several commands at the same time then monitor and change them with ease. You won't find this feature in guake or tilda!
Pro Tabs support
Yakuake supports tabs, while working with several tabs is very easy. By default: to open a new tab press Ctrl + Shift + t
. To move through them: Shift + left/right arrow
.
Pro Monitor for activity/silence
When an activity is let working (e.g.: compiling some source or upgrading some system), and you forgot it, a nice popup and sound will alert you when the command prompt returned on that term.
Pro Unlimited scroll history
You can scroll, inside the same terminal session, infinitely, so no command should be lost, even it isn't stored yet on history.
Pro Lightweight
Opens at 40MB and stays below 100MB with some tabs splitted in four each. So if you need to have many terminals emulators opened in your desktop environment, is the a very light solution for all the features it includes.
Pro Quick search support
Search directly in your favourite search engine just by selecting something and right clicking. It will open the browser result page.
Pro Quick move through splits and tabs
You can move through terminals with Ctrl+Shift+Cursors or tabs with Shift+Cursor keys, so no need to touch you mouse or pad, making working with terms even faster.
Pro Can be scripted using qdbus
Window composition and commands inside can be scripted using qdbus.
You can make desktop shortcuts to automatically create tabs, split windows and connect to ssh sessions or launch monitoring programms. Very useful.
Pro Wayland support
As the entire Plasma Desktop, yakuake already has full support for Wayland.
Pro Save output as text
You can save the output of a terminal directly to a text file, to work properly with it later.
Pro Enhanced focused terminal
You can configure yakuake to show a visual altert when you change the terminal. So even if you have many splittings and you don't use the mouse to change between them, you can easily see where you are at any moment.
Cons
Con Unicode characters that are too wide are blanked instead of clipped
If a character in a backup font is wider than the base font, urxvt substitutes the non-displayable character. A large letter space will show the wide characters, but the result is not reasonably spaced. There is a patch from 2014 that the urxvt maintainer will not merge.
Con Requires work to look acceptable
Out of the box, rxvt-unicode is not too pleasant to look at. Some understanding of Xresources is required for updating its appearance. That being said, the experience of customizing it can be very rewarding.

Con Requires work to configure useful functionality (clickable URL's, font scaling, tabs)
Con In daemon mode you can lose all your terminals
Because of sharing the same process terminal windows cannot be killed without sacrificing all other open windows. That becomes even more dangerous if you use multiple graphical managers without overriding socket with RXVT_SOCKET.
Con Unicode rendering is buggy
There are a few references to urxvt's buggy rendering, such as unicode combining characters, which bled through during scrolling.
Con Bloated
Exists because Xterm is complete trash. Although it has a lot of features, you will most likely never use them all.
Con No support yet for 24-bit "True Color"
Though this is still not available, you can download the patched version for 24bit, here.
Con Font size cannot be changed on the fly with the mousewheel
Sometimes you may need to enlarge the font to improve readability, or shrink it to have more real estate and "hawk's eye" view of data. In rxvt you need to change the configuration file or use these commands:
$ function fontsize
{printf '\33]50;%s%d\007' "xft:Dejavu Sans Mono:size=$1::antialias=false"}
$ fontsize 22
Con No option to have a "reverse color" cursor
While you can choose the color of the cursor and the character under the cursor, there's no automatic "reverse color" for the cursor. This makes it impossible to use rxvt-unicode if you have a light background terminal and a dark background editor.
Con Theming options are very limited, Does not integrate naturally with the DE
Con KDE Library dependencies
While not an issue if using KDE, when trying to use this terminal in other desktop environments or window managers, there will be a large amount of dependencies tied to the app. This makes for a large install size. For those trying to keep their desktop lean, this may be an issue.
Con No sessions support
Con No Windows support
Con Slow
Is not slow at all. I have yakuake installed in all my computers (8) and it launches immediatly after pressing the hotkey. Must be a error from yourt side.
Yakuake has started to get really slow with the latest updates: it takes up to 3 seconds to start up after you have clicked the assigned hotkey.
Con Heavy
Not true at all. I from far one of the lightiest graphical terminals out there. Mine is 14MB with a bunch of split views and 4 tabs at the moment of writing this.
