When comparing Xshell 6 vs rxvt-unicode, the Slant community recommends rxvt-unicode for most people. In the question“What is the best terminal emulator? ” rxvt-unicode is ranked 4th while Xshell 6 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 Connections management
Pro Has tabs
Pro Compose bar to send a string to multiple servers at once
Pro Local shell interface to control Xshell
Pro Great option for enterprises
Xshell 6 caters to enterprises with features such as multi-tab UI, dynamic port forwarding, scripting support, support for ASCII as well as non-ASCII characters, etc.
Pro Can use any system font
Pro Tunneling bar
Channel monitoring and dynamic port forwarding.
Pro User defined key map support
Pro Task automation with VB script
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
.
Cons
Con Not free
The subscription costs $89 per year.
Con No stable portable version
Any portable version present is wrapper. It moves files from portable folder to appdata and backward, which often cause dataloss
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.
